History of the Dmax
- Thread starter NinjaMax
- Start date
Rebuilding The 6.6L Duramax Diesel
In 1996, as General Motors was finalizing plans for its next generation of full-size trucks (code named GMT800), the company had only 3% market-share of the diesel-powered heavy-duty pick-up truck segment.
By Roy Berndt
It was really no surprise, since GM had single-handedly alienated the American buying public against the diesel engine beginning back in the late ’70s and early ’80s with the 5.7L V8 and 4.3L V6 diesel engines that were, let’s just say, “less than stellar.” While there’s no point now in rehashing mistakes of the past, the 6.2L and 6.5L diesels had continued on in a similar tradition, even though the 6.5L was used in the HUMVEE for the military.
In order to have a winning truck this time, GM needed to have a winning diesel powertrain. The General already had two strikes and a third may have put GM out of the diesel pick-up market altogether.
A small group of stakeholders led by the Planning Group reviewed proposals from numerous possible diesel engine manufacturers for the all-new truck. The decision was reached to go with a proposal from one of GM’s partners – Isuzu Motors LTD, a company founded in 1916 and, with a long history of successful diesel technology, recognized worldwide as a leader in diesel engines. The proposal was developed as a part of a strategic 90-day study conducted by Isuzu and GM, relative to Isuzu’s role in the GM Global enterprise.
While Isuzu’s plan called for a “Clean Sheet” brand new engine design that would not be ready until 2003, GM’s new HD pickup truck was going into production in late 2000. After high-level executive meetings, Isuzu found a way to pull ahead the timing to meet GM’s needs. In May 1997, the project team was established under the leadership of Jim Hogan, GM Truck Group; Yoshihiro Tadaki, Isuzu; and Jim Kerekes, representing GM Powertrain.
The project was codenamed “B908” (bridge between U.S. and Isuzu, 90-day study and 8-cylinders). This would be the first V8 diesel engine Isuzu ever designed for the U.S. HD pickup market. Isuzu was responsible for the base engine design and GM was responsible for the integration of the engine into the vehicle. The GM Powertrain – Romulus Engineering Lab became the center of activity in the U.S.
The first running B908 engines were available in early 1998 in Japan and soon were installed in mule vehicles in the U.S. to begin the final development. The B908 Team used the 13-hour time difference to their advantage. They would videoconference late in the day U.S. time while Japan would work on the issue during their day and when the U.S. team came in the next morning, have another videoconference to review and the US would work during their day while it was Japan’s night. It was truly 24/7 development.
The GM-Isuzu 90-day study established the plan to manufacture the new engine: a joint venture company named DMAX Ltd. (signifying the diesel engine and maximum power, cleanliness and fuel economy) was established in September, 1998 in Moraine, OH. A new 650,000 sq. ft. engine plant was built near the former 6.5L diesel engine plant, and many of the employees were able to transfer to the new joint venture.
The totally new engine design was a 6.6L, 90-degree, direct-injection, overhead valve, four-valve-per-cylinder, turbo-charged diesel V8 with aluminum high swirl cylinder heads. The electrically controlled common-rail fuel system provided maximum power for each pulse of fuel used and allowed full authority in injection timing and quantity. This combination along with pilot injection provided operating quietness and smoothness typical of similarly sized gasoline engines.
When it came time to decide upon the marketing name for the new B908 engine, GM was already handicapped by its poor diesel reputation. The name itself was critical, as it would compete against Ford’s established “Powerstroke” Diesel engine. Dodge was using the Cummins engine and needed no other name, so after many meetings the engine was named Duramax Diesel 6600. Like the joint venture name, “Duramax” was meant to highlight the durability and reliability of the new engine.
In late 2000 the Duramax Diesel 6600 debuted in the new 2001 HD pickup trucks. Brought to market in only 37 months, it was the fastest new engine developed by GM Powertrain – at that time. The engine was an immediate success, making Ward’s Magazine “10 Best Engines” both in 2001 and 2002, and bringing up GM’s market share from 3 percent to 30 percent in the HD Diesel pick-up truck market.
So now that we know how it got here, let’s take a look at the basic specs of this engine, the RPO designations and how the proliferation of the major engine components has taken place. In addition, we’ll highlight some of what you need to know and watch out for as you go through the remanufacturing of these engines.
Timeline:
2001 Duramax
The RPO LB7 (engine code “1”) was first introduced in 2001 and continued until 2004. This is a 32-valve design with high-pressure common-rail direct injection and aluminum cylinder heads. The most problematic issue with the LB7 is injector failure. Since the injectors are under the valve cover in the engine, lubricating oil fuel dilution occurred and often ended in a catastrophic engine failure. A class action lawsuit against GM resulted in an extended warranty for this situation for 7 year/200,000 mile coverage.
The following trucks use the LB7:
• Chevrolet Kodiak/GMC Topkick
• Chevrolet Silverado/GMC Sierra HD
Engine Specs:
• Engine type: 6,599 cc (6.599 L; 402.7 cu in) V8 turbo
• Bore x Stroke: 4.06˝ (103.1 mm) x 3.90˝ (99.1 mm)
• Block/Head: Cast gray iron/cast aluminum
• Aspiration: Turbocharged & Intercooled
• Valvetrain: OHV 4-V
• Compression: 17.5:1
• Injection: Direct; Bosch High Pressure Common-rail
• Power/Torque: 300 bhp (220 kW) @ 3100 rpm / 520 lb-ft (705 N•m) @ 1800 rpm.
2004 Duramax
The RPO LLY (internally called the 8GF1 – engine code “2”) debuted in mid-2004 and continued until the end of 2005. The LLY was GM’s first attempt to implement emissions requirements on its diesel trucks. To meet this goal GM turned to a newly developed Garrett turbocharger with a variable geometry vane system and installed an Exhaust Gas
Recirculation valve. Learning from problems with injectors in the previous LB7, GM changed the valve covers to not only remove them from the engine oiling system but allow access to the injectors without having to remove the valve covers.
Early on, problems came forward from customers complaining of severe overheating, and, in some situations, blown head gaskets. Although initially GM denied that it was a problem, after it was sued by a consumer group it relented and included overheating and blown head gaskets as a warranted item.
The following trucks used the LLY engine:
• 2006 Hummer H1 Alpha
• Chevrolet Silverado/GMC Sierra HD
Engine Spec changes:
• Power / Torque: 310 bhp (230 kW) @ 3000rpm / 590 lb•ft (800 N•m) @ 1600 rpm
• Head casting is c/n 8gf1
• Block casting is c/n 22351021213
2006 Duramax
RPO 2006 LLY (engine code “2”) debuted in the beginning of 2006 and ended production with the start of the 2007 calendar year. While it retained the LLY designation, mechanically it is identical to the LBZ and is mated to the new 6-speed Allison transmission.
RPO LBZ (engine code “D”) debuted in late 2006 and continued into 2007, sold only in the “classic” body style. It has a more powerful tune loaded into the computer that allows it to produce more power and torque.
Changes include:
• Cylinder block casting and machining changes strengthen the bottom of the cylinder bores to support increased power and torque
• Upgraded main bearing material increases durability
• Revised piston design helps lower compression ratio to 16.8:1 from 17.5:1
• Piston pin length was increased for increased strength
• Connecting rod “I” section is thicker for increased strength
• Cylinder heads revised to accommodate lower compression and reduced cylinder firing pressure
• Maximum injection pressure increased from 23,000 psi (1,585.8 bar) to more than 26,000 psi (1,792.6 bar)
• Fuel delivered via higher-pressure pump, fuel rails, distribution lines and all-new, seven-hole fuel injectors
• Fuel injectors spray directly onto glow plugs, providing faster, better-quality starts and more complete cold-start combustion for reduced emissions
• Improved glow plugs heat up faster through an independent controller
• Revised variable-geometry turbocharger is aerodynamically more efficient to help deliver smooth and immediate response and lower emissions
• Air induction system re-tuned to enhance quietness
• EGR has larger cooler to bring more exhaust into the system
• First application of new, 32-bit E35 controller, which adjusts and compensates for the fuel flow to bolster efficiency and reduce emissions.
LBZ applications:
• Chevrolet Silverado HD
• Chevrolet Kodiak
• GMC Sierra HD
• GMC TopKick
LLY applications:
• Chevrolet Silverado HD
• Chevrolet Kodiak
• GMC Sierra HD
• Chevy Express full-size (reduced power output mated to a 4l85E transmission)
• GMC Savanna full-size (reduced power output mated to a 4l85E transmission)
Engine Specification changes:
• Compression: 16.8:1
• Injection: Bosch High Pressure Common-rail
• For a chart explaining the Power/Torque relationships in this model year, see the enhanced version online. Details at the end of this article.
2007 Duramax
RPO LMM engines (engine code “6”) are based on the LBZ engines, but were designed for U.S. EPA’s 2007 emission standards, and uses ultra-low sulfur diesel fuel, which went on sale in the US and Canada in the fall of 2006.
New emission reduction features include a Diesel Particulate Filter (DPF), which traps particulate matter. When the computer senses a pressure differential between two sensors (one located upstream and another downstream of the DPF) the truck enters a “regeneration” cycle.
During this time the computer commands the fuel injectors to inject fuel after the cylinder has fired, forcing raw fuel into the DOC (Diesel Oxidizing Catalyst) where it is burned to elevate the temperature of the exhaust. This hot exhaust then flows into the DPF and burns the trapped soot.
•Compression: 15.8:1
•Injection: Bosch High Pressure Common Rail with CP3.3 Injection Pump
•Power / Torque: 365 bhp (272 kW) @ 3200rpm / 660 lb•ft (895 N•m) @1600 rpm
Emission controls:
•Additional combustion control, including an even more efficient variable-geometry turbocharging system, cooled (enhanced) exhaust gas recirculation (EGR) and closed crankcase ventilation to reduce nitrogen oxides (NOx)
•Additional exhaust control, including oxidizing catalyst and new diesel particulate filter (DPF) to reduce soot and particulate matter
•Increased-capacity cooling system
•New engine control software
•Use of low-ash engine oil (CJ-4)
LMM Applications
•2007- Chevrolet Silverado HD[8]
•2007- GMC Sierra HD
•Chevrolet Kodiak
•GMC Topkick
•Chevrolet Express/GMC Savanna
Current Duramax Versions
RPO LML (VIN code “8”) is the latest version (2011 - present) of the Isuzu/GM Duramax V8 diesel engine and is actually a more advanced version of the LMM engine. The majority of the changes addressing a required drastic reduction in engine emissions. Some mechanical aspects of the engine, such as piston oil flow design for improved temperature control and oil pump design, were also improved to enhance durability even further.
The LML engine was significantly updated for 2011 to provide improved exhaust emissions that comply with the new federal emission standards for diesel engines, provide better engine rigidity and further noise reduction. New 29,000 PSI piezo injectors, a complete fuel system-hardening to tolerate up to 20% biodiesel mixtures and urea injection (to reduce Nitrogen oxides) with a 5.8 gallon urea tank are updating the fuel and emissions systems. This engine now 9 has fuel injectors, one directly injecting in the exhaust tract, to allow raw fuel injection during the particulate filter recycling routine.
This was previously accomplished by running raw fuel through the engine via the engine fuel injectors without igniting the fuel (valves were kept open), but risks of washing down cylinder walls and causing engine damage are increased with the use of Biodiesel. The RPO LML engine is rated at 397 horsepower at 3000 rpm and 765 lb.-ft. of torque at 1600 rpm.
RPO LGH 6.6L Duramax diesel engine (VIN code “L”) is used on 2010 interim and 2011 Chevrolet Express and GMC Savana vans and 2011 Chevrolet Silverado and GMC Sierra trucks with RPO ZW9 (chassis cabs or trucks with pickup box delete). The LGH engine is rated at 335 bhp (250 kW) at 3100 rpm and 685 lb•ft (929 N•m) at 1600 rpm.
RPO LMK This engine is not yet commercially launched although it was touted in the automobile press as one of the most important new engine concepts for small trucks and SUVs by finally delivering a capable diesel engine in a compact enough package. General Motors planned a 4.5 liter 72-degree V8 for light-duty applications which would be built at GM's powertrain facility in Tonawanda, New York after 2009. Designed to fit in the same space as a Chevrolet Small-Block engine, it is expected to produce over 310 bhp (230 kW) and 520 lb•ft (705 N•m) of torque. It added urea injection, 29,000-psi (2,000 bar) piezo-electric common-rail fuel system over previous Duramax architecture.
It was initially targeted for the Chevy Silverado/GMC Sierra and Hummer H2. Unlike previous Duramax engines, the 4.5 liter is planned to be designed and built entirely by GM, without assistance from Isuzu.
As of March 2009, a GM spokesperson stated the engine project has been put on an “indefinite hold” due to current economic conditions. It is a shame that this engine has not yet materialized since it could have been GM’s ace in their sleeve. To date there are no diesels in what used to be classified as the half-ton truck market that would have a diesel available. If the Ford F-150 beats GM to the punch they will have squandered an opportunity of major proportion to take the lead.
CYLINDER BLOCKS
In typical import manufacturing fashion, production casting numbers do not necessarily give you what you would call a definitive identifier. That is why it is so important to know the specific casting identifiers. It is my intent to provide you with that information to correctly understand the proliferation by sight and not casting number.
The Duramax cylinder blocks are pretty simple to identify, since there are only two of them.
The first block casting was used from the original release through the end of 2005 MY of production. It is easily identified by the difference where the water pump bolts to the block and the bolt bosses (or absence thereof ). See Figure 1.
The second block has the additional bosses and also uses longer main bearing bolts. The main bearing bolt used in ’05 MY and earlier is approximately 4-¼˝ long. The bolts used in ’06 MY and later are approximately 4-½˝ long.
The water pump mounting bolts changed but so did the water pump. There is a larger output and higher volume water pump being used (see Figure 2) as seen by the difference of the output outlet.
CRANKSHAFT
Crankshafts for the D-Max are forged steel with a nitride heat treatment. The nitride hard face provides a strong wearresistant bearing face that has a high lubricity quality, an excellent surface for aluminum alloy shell-type bearings.
The downside is that the affected area is very shallow and ANY undersize grinding will require the crankshaft to be re-nitride treated. This is NOT an option: if the crankshaft is not re-treated it will fail 100% of the time. There are even those of the opinion that too heavy of a polish will give you an issue as well, so the handling of these crankshafts with the utmost care is critical.
SRC (Springfield Remanufacturing Company) actually made specific stackable wooden dunage that can house the cranks so that there is never any chance of journal “ding” damage. My cautions may seem like overkill but premature D-Max bearing failure warranties can cost you a considerable amount very quickly.
There are two crankshafts for the D-Max up through ’05 MY and ’06 MY and later. There is a difference in their balance and their differences are very subtle. There are a couple of “bumps” in the forging in the area just off the second and fourth main bearing journal area (see Figure 3) for the ’06 MY and later parts, but dimensionally the two cranks are identical.
CAMSHAFTS
Camshafts are easy to identify: they are all the same, except for the timing gears. As shown in Figure 4,
the early timing gears (through ’05 MY) were solid and ’06 MY and later used a split gear that is spring loaded to avoid any type timing gear train noise These camshafts are rifle drilled and will, on occasion, break. It’s not chronic but it is something to be aware of. They are relatively inexpensive and SRC replaces them 100%
ROCKER ARMS, CAM FOLLOWERS AND PUSHRODS
The same ’05 MY and ’06 MY break for changes applies to the rocker arms, cam followers and pushrods. Through ’05 MY the pushrods were solid and did not have oil running through them. Beginning in ‘06 MY the push rods were hollow and did have oil running through them. Rocker arm oiling holes changed from .110˝ to .150˝. The cam followers changed to a larger diameter pin that the roller would rotate on as it followed the cam lobe. This lifter also had provisions to feed oil through the pushrod (see Figure 5).
CONNECTING RODS
Connecting rods are pretty much the same story as the other components. Used through ’05 MY, the first generation connecting rod has a lighter beam and shorter wrist pin. The second connecting rod (’06 MY and later) has a dimple on the beam and has a heavier beam and longer wrist pin.
PISTONS
The pistons follow suit with the rods. The different model years obviously had a pin length change and they have different compression ratios. Visually, they are unmistakable (as seen in Figure 6). The later piston is scalloped and had bushings for the wrist pin, and has a graphite coating on the skirt.
CYLINDER HEAD, VALVE COVERS, INJECTORS AND GLOW PLUGS
This is the only area that may get a bit confusing. There are three cylinder heads and they do not follow as clean a break as the rest of the components. However, these guidelines should make it easy for you.
The first cylinder head was used through mid-’04 MY and had the injectors under the valve cover. The problem was, if an injector went bad it contaminated the lubricating oil and often the result would be a catastrophic engine failure. This cylinder head is easily identified by the valve cover rail being around the perimeter of the cylinder head (seeFigure 7) and the fact that the injectors sit way down in the cylinder head between the four valves.
The second cylinder head, which came into being mid-’04 MY, had the revised valve cover and the new injector that was now outside of the lubricating oil (see Figure 8). This model head is easily recognized
not only by the cover but the injector is longer and the mounting surface is a raised boss that you cannot mistake.
The third and final cylinder head (used from ’06 MY-current) looks very similar to the second design cylinder head. The only distinct identifier is the glow plug hole, which uses a different thread so that it cannot be installed in the previous cylinder head.
There have been two basic Duramax valve covers used, if you discount the crankcase ventilation differences (see Figure 9). A larger, normal looking cover that had the injectors underneath was used through mid-’04 MY. The second looks like a pretzel project gone bad. Injectors are out of the cover with no chance of contaminating the lubricating oil. This second cover also went through various renditions of emissions experimentation, with the orifice sizes for the crankcase ventilation changing from .370˝ to .465˝ to, lastly, .560˝. If you replace a cover, know which hole you have for crankcase ventilation.
The Duramax had two different fuel injector body types. The one that sat under the valve cover is shorter and in the lubricating oil. The injector that now sits outside the valve cover is quite a bit longer and there is no way to mix them up or put one in the wrong head (see Figure 10) for proper identification).
Three different glow plugs were used to correspond with the three different cylinder heads (see Figure 11).
The first series glow plug and the second one (used in the mid-’04 MY through ’05 MY engines) look identical but have different voltages. The early production is 11 volt and the mid-’04 MY is 4.7 volt. The barrels have the voltage marked on them so do not inter-mix these glow plugs or there will be problems. Either the engine will not start or you will be burning up your glow plugs. The ’04 MY injector and the ’06 and later glow plugs are actually the same glow plug but the ’06 MY has the threads about midway down the body. As stated earlier, the glow plug hole is the major difference between the two cylinder heads.
Things worth noting:
• The oil pump drive gear went from right hand to left hand thread in ’06 MY. The premise behind the decision was that the engine rotation could potentially loosen the nut, although I have found no one to confirm that had ever happened. However, once it was changed so that the engine’s natural rotation would keep the nut tight there ARE reports of that happening. This locks up the oil pump, so the rest I leave to your imagination.
• The camshaft has a negative ramp on the lobe.
• D-Max has apparently solved the issue of valve seat inserts falling out of aluminum cylinder heads. The incidence of occurrence is near zero.
• The increased glow plug length design allows for injection to fire directly across the glow plug. Injectors fire off five burst during each combustion cycle.
• The use of a variable vane turbo allows for high torque at low RPM and spools the turbo up quicker.
Special Thanks:
A special thanks goes out to all those at SRC (Springfield Remanufacturing Corp., Springfield, MO) who helped with the information gathering process. SRC had its early beginnings similar to Franklin Power in that they were both IHC (International Harvester Corporation) authorized “ReNew” centers which meant that they remanufactured for IHC. SRC purchased the business from IHC in 1983 and has now grown to a major OE provider of both gasoline and diesel engines. SRC is also a partner in a recent Case New Holland remanufacturing venture just starting up.
Something that you do not see very often in a major remanufacturing facility is that it is climate controlled. SRC’s ability to maintain production levels and quality in the blistering hot Ozark summers speaks volumes of their commitment to the product and their employees. My visitation was at the diesel facility and the hospitality and sharing was as unselfish as it comes. I met with Ryan Stack, a recent addition in running the plant, a gentleman certainly cut from the same cloth as his father, Jack Stack. Many of you know Jack as a speaker and author, and someone passionate about the company.
SRC is a quality organization that has a “do it right” spirit seen through the facility. The company obviously believes in major reinvestment into the infrastructure as witnessed by the technology of CNC equipment throughout the facility. Finally, I would be remiss if I did not mention Nick Greer, who was the meat and potatoes guy in obtaining this information
In 1996, as General Motors was finalizing plans for its next generation of full-size trucks (code named GMT800), the company had only 3% market-share of the diesel-powered heavy-duty pick-up truck segment.
By Roy Berndt
It was really no surprise, since GM had single-handedly alienated the American buying public against the diesel engine beginning back in the late ’70s and early ’80s with the 5.7L V8 and 4.3L V6 diesel engines that were, let’s just say, “less than stellar.” While there’s no point now in rehashing mistakes of the past, the 6.2L and 6.5L diesels had continued on in a similar tradition, even though the 6.5L was used in the HUMVEE for the military.
In order to have a winning truck this time, GM needed to have a winning diesel powertrain. The General already had two strikes and a third may have put GM out of the diesel pick-up market altogether.
A small group of stakeholders led by the Planning Group reviewed proposals from numerous possible diesel engine manufacturers for the all-new truck. The decision was reached to go with a proposal from one of GM’s partners – Isuzu Motors LTD, a company founded in 1916 and, with a long history of successful diesel technology, recognized worldwide as a leader in diesel engines. The proposal was developed as a part of a strategic 90-day study conducted by Isuzu and GM, relative to Isuzu’s role in the GM Global enterprise.
While Isuzu’s plan called for a “Clean Sheet” brand new engine design that would not be ready until 2003, GM’s new HD pickup truck was going into production in late 2000. After high-level executive meetings, Isuzu found a way to pull ahead the timing to meet GM’s needs. In May 1997, the project team was established under the leadership of Jim Hogan, GM Truck Group; Yoshihiro Tadaki, Isuzu; and Jim Kerekes, representing GM Powertrain.
The project was codenamed “B908” (bridge between U.S. and Isuzu, 90-day study and 8-cylinders). This would be the first V8 diesel engine Isuzu ever designed for the U.S. HD pickup market. Isuzu was responsible for the base engine design and GM was responsible for the integration of the engine into the vehicle. The GM Powertrain – Romulus Engineering Lab became the center of activity in the U.S.
The first running B908 engines were available in early 1998 in Japan and soon were installed in mule vehicles in the U.S. to begin the final development. The B908 Team used the 13-hour time difference to their advantage. They would videoconference late in the day U.S. time while Japan would work on the issue during their day and when the U.S. team came in the next morning, have another videoconference to review and the US would work during their day while it was Japan’s night. It was truly 24/7 development.
The GM-Isuzu 90-day study established the plan to manufacture the new engine: a joint venture company named DMAX Ltd. (signifying the diesel engine and maximum power, cleanliness and fuel economy) was established in September, 1998 in Moraine, OH. A new 650,000 sq. ft. engine plant was built near the former 6.5L diesel engine plant, and many of the employees were able to transfer to the new joint venture.
The totally new engine design was a 6.6L, 90-degree, direct-injection, overhead valve, four-valve-per-cylinder, turbo-charged diesel V8 with aluminum high swirl cylinder heads. The electrically controlled common-rail fuel system provided maximum power for each pulse of fuel used and allowed full authority in injection timing and quantity. This combination along with pilot injection provided operating quietness and smoothness typical of similarly sized gasoline engines.
When it came time to decide upon the marketing name for the new B908 engine, GM was already handicapped by its poor diesel reputation. The name itself was critical, as it would compete against Ford’s established “Powerstroke” Diesel engine. Dodge was using the Cummins engine and needed no other name, so after many meetings the engine was named Duramax Diesel 6600. Like the joint venture name, “Duramax” was meant to highlight the durability and reliability of the new engine.
In late 2000 the Duramax Diesel 6600 debuted in the new 2001 HD pickup trucks. Brought to market in only 37 months, it was the fastest new engine developed by GM Powertrain – at that time. The engine was an immediate success, making Ward’s Magazine “10 Best Engines” both in 2001 and 2002, and bringing up GM’s market share from 3 percent to 30 percent in the HD Diesel pick-up truck market.
So now that we know how it got here, let’s take a look at the basic specs of this engine, the RPO designations and how the proliferation of the major engine components has taken place. In addition, we’ll highlight some of what you need to know and watch out for as you go through the remanufacturing of these engines.
Timeline:
2001 Duramax
The RPO LB7 (engine code “1”) was first introduced in 2001 and continued until 2004. This is a 32-valve design with high-pressure common-rail direct injection and aluminum cylinder heads. The most problematic issue with the LB7 is injector failure. Since the injectors are under the valve cover in the engine, lubricating oil fuel dilution occurred and often ended in a catastrophic engine failure. A class action lawsuit against GM resulted in an extended warranty for this situation for 7 year/200,000 mile coverage.
The following trucks use the LB7:
• Chevrolet Kodiak/GMC Topkick
• Chevrolet Silverado/GMC Sierra HD
Engine Specs:
• Engine type: 6,599 cc (6.599 L; 402.7 cu in) V8 turbo
• Bore x Stroke: 4.06˝ (103.1 mm) x 3.90˝ (99.1 mm)
• Block/Head: Cast gray iron/cast aluminum
• Aspiration: Turbocharged & Intercooled
• Valvetrain: OHV 4-V
• Compression: 17.5:1
• Injection: Direct; Bosch High Pressure Common-rail
• Power/Torque: 300 bhp (220 kW) @ 3100 rpm / 520 lb-ft (705 N•m) @ 1800 rpm.
2004 Duramax
The RPO LLY (internally called the 8GF1 – engine code “2”) debuted in mid-2004 and continued until the end of 2005. The LLY was GM’s first attempt to implement emissions requirements on its diesel trucks. To meet this goal GM turned to a newly developed Garrett turbocharger with a variable geometry vane system and installed an Exhaust Gas
Recirculation valve. Learning from problems with injectors in the previous LB7, GM changed the valve covers to not only remove them from the engine oiling system but allow access to the injectors without having to remove the valve covers.
Early on, problems came forward from customers complaining of severe overheating, and, in some situations, blown head gaskets. Although initially GM denied that it was a problem, after it was sued by a consumer group it relented and included overheating and blown head gaskets as a warranted item.
The following trucks used the LLY engine:
• 2006 Hummer H1 Alpha
• Chevrolet Silverado/GMC Sierra HD
Engine Spec changes:
• Power / Torque: 310 bhp (230 kW) @ 3000rpm / 590 lb•ft (800 N•m) @ 1600 rpm
• Head casting is c/n 8gf1
• Block casting is c/n 22351021213
2006 Duramax
RPO 2006 LLY (engine code “2”) debuted in the beginning of 2006 and ended production with the start of the 2007 calendar year. While it retained the LLY designation, mechanically it is identical to the LBZ and is mated to the new 6-speed Allison transmission.
RPO LBZ (engine code “D”) debuted in late 2006 and continued into 2007, sold only in the “classic” body style. It has a more powerful tune loaded into the computer that allows it to produce more power and torque.
Changes include:
• Cylinder block casting and machining changes strengthen the bottom of the cylinder bores to support increased power and torque
• Upgraded main bearing material increases durability
• Revised piston design helps lower compression ratio to 16.8:1 from 17.5:1
• Piston pin length was increased for increased strength
• Connecting rod “I” section is thicker for increased strength
• Cylinder heads revised to accommodate lower compression and reduced cylinder firing pressure
• Maximum injection pressure increased from 23,000 psi (1,585.8 bar) to more than 26,000 psi (1,792.6 bar)
• Fuel delivered via higher-pressure pump, fuel rails, distribution lines and all-new, seven-hole fuel injectors
• Fuel injectors spray directly onto glow plugs, providing faster, better-quality starts and more complete cold-start combustion for reduced emissions
• Improved glow plugs heat up faster through an independent controller
• Revised variable-geometry turbocharger is aerodynamically more efficient to help deliver smooth and immediate response and lower emissions
• Air induction system re-tuned to enhance quietness
• EGR has larger cooler to bring more exhaust into the system
• First application of new, 32-bit E35 controller, which adjusts and compensates for the fuel flow to bolster efficiency and reduce emissions.
LBZ applications:
• Chevrolet Silverado HD
• Chevrolet Kodiak
• GMC Sierra HD
• GMC TopKick
LLY applications:
• Chevrolet Silverado HD
• Chevrolet Kodiak
• GMC Sierra HD
• Chevy Express full-size (reduced power output mated to a 4l85E transmission)
• GMC Savanna full-size (reduced power output mated to a 4l85E transmission)
Engine Specification changes:
• Compression: 16.8:1
• Injection: Bosch High Pressure Common-rail
• For a chart explaining the Power/Torque relationships in this model year, see the enhanced version online. Details at the end of this article.
2007 Duramax
RPO LMM engines (engine code “6”) are based on the LBZ engines, but were designed for U.S. EPA’s 2007 emission standards, and uses ultra-low sulfur diesel fuel, which went on sale in the US and Canada in the fall of 2006.
New emission reduction features include a Diesel Particulate Filter (DPF), which traps particulate matter. When the computer senses a pressure differential between two sensors (one located upstream and another downstream of the DPF) the truck enters a “regeneration” cycle.
During this time the computer commands the fuel injectors to inject fuel after the cylinder has fired, forcing raw fuel into the DOC (Diesel Oxidizing Catalyst) where it is burned to elevate the temperature of the exhaust. This hot exhaust then flows into the DPF and burns the trapped soot.
•Compression: 15.8:1
•Injection: Bosch High Pressure Common Rail with CP3.3 Injection Pump
•Power / Torque: 365 bhp (272 kW) @ 3200rpm / 660 lb•ft (895 N•m) @1600 rpm
Emission controls:
•Additional combustion control, including an even more efficient variable-geometry turbocharging system, cooled (enhanced) exhaust gas recirculation (EGR) and closed crankcase ventilation to reduce nitrogen oxides (NOx)
•Additional exhaust control, including oxidizing catalyst and new diesel particulate filter (DPF) to reduce soot and particulate matter
•Increased-capacity cooling system
•New engine control software
•Use of low-ash engine oil (CJ-4)
LMM Applications
•2007- Chevrolet Silverado HD[8]
•2007- GMC Sierra HD
•Chevrolet Kodiak
•GMC Topkick
•Chevrolet Express/GMC Savanna
Current Duramax Versions
RPO LML (VIN code “8”) is the latest version (2011 - present) of the Isuzu/GM Duramax V8 diesel engine and is actually a more advanced version of the LMM engine. The majority of the changes addressing a required drastic reduction in engine emissions. Some mechanical aspects of the engine, such as piston oil flow design for improved temperature control and oil pump design, were also improved to enhance durability even further.
The LML engine was significantly updated for 2011 to provide improved exhaust emissions that comply with the new federal emission standards for diesel engines, provide better engine rigidity and further noise reduction. New 29,000 PSI piezo injectors, a complete fuel system-hardening to tolerate up to 20% biodiesel mixtures and urea injection (to reduce Nitrogen oxides) with a 5.8 gallon urea tank are updating the fuel and emissions systems. This engine now 9 has fuel injectors, one directly injecting in the exhaust tract, to allow raw fuel injection during the particulate filter recycling routine.
This was previously accomplished by running raw fuel through the engine via the engine fuel injectors without igniting the fuel (valves were kept open), but risks of washing down cylinder walls and causing engine damage are increased with the use of Biodiesel. The RPO LML engine is rated at 397 horsepower at 3000 rpm and 765 lb.-ft. of torque at 1600 rpm.
RPO LGH 6.6L Duramax diesel engine (VIN code “L”) is used on 2010 interim and 2011 Chevrolet Express and GMC Savana vans and 2011 Chevrolet Silverado and GMC Sierra trucks with RPO ZW9 (chassis cabs or trucks with pickup box delete). The LGH engine is rated at 335 bhp (250 kW) at 3100 rpm and 685 lb•ft (929 N•m) at 1600 rpm.
RPO LMK This engine is not yet commercially launched although it was touted in the automobile press as one of the most important new engine concepts for small trucks and SUVs by finally delivering a capable diesel engine in a compact enough package. General Motors planned a 4.5 liter 72-degree V8 for light-duty applications which would be built at GM's powertrain facility in Tonawanda, New York after 2009. Designed to fit in the same space as a Chevrolet Small-Block engine, it is expected to produce over 310 bhp (230 kW) and 520 lb•ft (705 N•m) of torque. It added urea injection, 29,000-psi (2,000 bar) piezo-electric common-rail fuel system over previous Duramax architecture.
It was initially targeted for the Chevy Silverado/GMC Sierra and Hummer H2. Unlike previous Duramax engines, the 4.5 liter is planned to be designed and built entirely by GM, without assistance from Isuzu.
As of March 2009, a GM spokesperson stated the engine project has been put on an “indefinite hold” due to current economic conditions. It is a shame that this engine has not yet materialized since it could have been GM’s ace in their sleeve. To date there are no diesels in what used to be classified as the half-ton truck market that would have a diesel available. If the Ford F-150 beats GM to the punch they will have squandered an opportunity of major proportion to take the lead.
CYLINDER BLOCKS
In typical import manufacturing fashion, production casting numbers do not necessarily give you what you would call a definitive identifier. That is why it is so important to know the specific casting identifiers. It is my intent to provide you with that information to correctly understand the proliferation by sight and not casting number.
The Duramax cylinder blocks are pretty simple to identify, since there are only two of them.
The first block casting was used from the original release through the end of 2005 MY of production. It is easily identified by the difference where the water pump bolts to the block and the bolt bosses (or absence thereof ). See Figure 1.
The second block has the additional bosses and also uses longer main bearing bolts. The main bearing bolt used in ’05 MY and earlier is approximately 4-¼˝ long. The bolts used in ’06 MY and later are approximately 4-½˝ long.
The water pump mounting bolts changed but so did the water pump. There is a larger output and higher volume water pump being used (see Figure 2) as seen by the difference of the output outlet.
CRANKSHAFT
Crankshafts for the D-Max are forged steel with a nitride heat treatment. The nitride hard face provides a strong wearresistant bearing face that has a high lubricity quality, an excellent surface for aluminum alloy shell-type bearings.
The downside is that the affected area is very shallow and ANY undersize grinding will require the crankshaft to be re-nitride treated. This is NOT an option: if the crankshaft is not re-treated it will fail 100% of the time. There are even those of the opinion that too heavy of a polish will give you an issue as well, so the handling of these crankshafts with the utmost care is critical.
SRC (Springfield Remanufacturing Company) actually made specific stackable wooden dunage that can house the cranks so that there is never any chance of journal “ding” damage. My cautions may seem like overkill but premature D-Max bearing failure warranties can cost you a considerable amount very quickly.
There are two crankshafts for the D-Max up through ’05 MY and ’06 MY and later. There is a difference in their balance and their differences are very subtle. There are a couple of “bumps” in the forging in the area just off the second and fourth main bearing journal area (see Figure 3) for the ’06 MY and later parts, but dimensionally the two cranks are identical.
CAMSHAFTS
Camshafts are easy to identify: they are all the same, except for the timing gears. As shown in Figure 4,
the early timing gears (through ’05 MY) were solid and ’06 MY and later used a split gear that is spring loaded to avoid any type timing gear train noise These camshafts are rifle drilled and will, on occasion, break. It’s not chronic but it is something to be aware of. They are relatively inexpensive and SRC replaces them 100%
ROCKER ARMS, CAM FOLLOWERS AND PUSHRODS
The same ’05 MY and ’06 MY break for changes applies to the rocker arms, cam followers and pushrods. Through ’05 MY the pushrods were solid and did not have oil running through them. Beginning in ‘06 MY the push rods were hollow and did have oil running through them. Rocker arm oiling holes changed from .110˝ to .150˝. The cam followers changed to a larger diameter pin that the roller would rotate on as it followed the cam lobe. This lifter also had provisions to feed oil through the pushrod (see Figure 5).
CONNECTING RODS
Connecting rods are pretty much the same story as the other components. Used through ’05 MY, the first generation connecting rod has a lighter beam and shorter wrist pin. The second connecting rod (’06 MY and later) has a dimple on the beam and has a heavier beam and longer wrist pin.
PISTONS
The pistons follow suit with the rods. The different model years obviously had a pin length change and they have different compression ratios. Visually, they are unmistakable (as seen in Figure 6). The later piston is scalloped and had bushings for the wrist pin, and has a graphite coating on the skirt.
CYLINDER HEAD, VALVE COVERS, INJECTORS AND GLOW PLUGS
This is the only area that may get a bit confusing. There are three cylinder heads and they do not follow as clean a break as the rest of the components. However, these guidelines should make it easy for you.
The first cylinder head was used through mid-’04 MY and had the injectors under the valve cover. The problem was, if an injector went bad it contaminated the lubricating oil and often the result would be a catastrophic engine failure. This cylinder head is easily identified by the valve cover rail being around the perimeter of the cylinder head (seeFigure 7) and the fact that the injectors sit way down in the cylinder head between the four valves.
The second cylinder head, which came into being mid-’04 MY, had the revised valve cover and the new injector that was now outside of the lubricating oil (see Figure 8). This model head is easily recognized
not only by the cover but the injector is longer and the mounting surface is a raised boss that you cannot mistake.
The third and final cylinder head (used from ’06 MY-current) looks very similar to the second design cylinder head. The only distinct identifier is the glow plug hole, which uses a different thread so that it cannot be installed in the previous cylinder head.
There have been two basic Duramax valve covers used, if you discount the crankcase ventilation differences (see Figure 9). A larger, normal looking cover that had the injectors underneath was used through mid-’04 MY. The second looks like a pretzel project gone bad. Injectors are out of the cover with no chance of contaminating the lubricating oil. This second cover also went through various renditions of emissions experimentation, with the orifice sizes for the crankcase ventilation changing from .370˝ to .465˝ to, lastly, .560˝. If you replace a cover, know which hole you have for crankcase ventilation.
The Duramax had two different fuel injector body types. The one that sat under the valve cover is shorter and in the lubricating oil. The injector that now sits outside the valve cover is quite a bit longer and there is no way to mix them up or put one in the wrong head (see Figure 10) for proper identification).
Three different glow plugs were used to correspond with the three different cylinder heads (see Figure 11).
The first series glow plug and the second one (used in the mid-’04 MY through ’05 MY engines) look identical but have different voltages. The early production is 11 volt and the mid-’04 MY is 4.7 volt. The barrels have the voltage marked on them so do not inter-mix these glow plugs or there will be problems. Either the engine will not start or you will be burning up your glow plugs. The ’04 MY injector and the ’06 and later glow plugs are actually the same glow plug but the ’06 MY has the threads about midway down the body. As stated earlier, the glow plug hole is the major difference between the two cylinder heads.
Things worth noting:
• The oil pump drive gear went from right hand to left hand thread in ’06 MY. The premise behind the decision was that the engine rotation could potentially loosen the nut, although I have found no one to confirm that had ever happened. However, once it was changed so that the engine’s natural rotation would keep the nut tight there ARE reports of that happening. This locks up the oil pump, so the rest I leave to your imagination.
• The camshaft has a negative ramp on the lobe.
• D-Max has apparently solved the issue of valve seat inserts falling out of aluminum cylinder heads. The incidence of occurrence is near zero.
• The increased glow plug length design allows for injection to fire directly across the glow plug. Injectors fire off five burst during each combustion cycle.
• The use of a variable vane turbo allows for high torque at low RPM and spools the turbo up quicker.
Special Thanks:
A special thanks goes out to all those at SRC (Springfield Remanufacturing Corp., Springfield, MO) who helped with the information gathering process. SRC had its early beginnings similar to Franklin Power in that they were both IHC (International Harvester Corporation) authorized “ReNew” centers which meant that they remanufactured for IHC. SRC purchased the business from IHC in 1983 and has now grown to a major OE provider of both gasoline and diesel engines. SRC is also a partner in a recent Case New Holland remanufacturing venture just starting up.
Something that you do not see very often in a major remanufacturing facility is that it is climate controlled. SRC’s ability to maintain production levels and quality in the blistering hot Ozark summers speaks volumes of their commitment to the product and their employees. My visitation was at the diesel facility and the hospitality and sharing was as unselfish as it comes. I met with Ryan Stack, a recent addition in running the plant, a gentleman certainly cut from the same cloth as his father, Jack Stack. Many of you know Jack as a speaker and author, and someone passionate about the company.
SRC is a quality organization that has a “do it right” spirit seen through the facility. The company obviously believes in major reinvestment into the infrastructure as witnessed by the technology of CNC equipment throughout the facility. Finally, I would be remiss if I did not mention Nick Greer, who was the meat and potatoes guy in obtaining this information
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Good read!! My company ( Paul's Machine&Welding) has sent a select group of us to SRC for the SRC Experience. We have implemented the Great Game Of Business in our company. Sorry. never the less. SRC is a incredible company. Ironically enough.. The lb7 currently in my truck came from SRC.( Heavy Duty Plant) As it has a tag stamped on the Dr. Side of it from the. Just crazy all the way around. But....... One heck of a read and thx for the Info.
I remember reading that article a while back and thought it was incredibly interesting. Specifically because it covers aspects of the engine that are not mentioned in any of the other dozens of run-of-the-mill "about the duramax" articles. Particularly about the 90-day engine design, and using the time difference to their advantage.
To think that, here we are, 15 years later still using the same basic engine design that was put together in 3 months, through all of the emissions changes etc. is pretty incredible, and a strong testament to GM Powertain/Isuzu's competency in engine design.
Couple little incorrect facts in there, but mostly a very good article. LBZ and LMM have the same compression ratio (16.8:1). And Ive never heard of Duramax's breaking camshafts. I think the LMM heads were mostly the same as LBZ, but have some minor differences. Guy would be the one to ask about that.
And then it has obviously not been updated for LML stuff...2011+ LML uses updated block, crank, rods, heads, pistons, fuel system, turbo, and engine controller. Camshaft is the same though as far as I know. I thought I heard somewhere that the LML has a CGI block, but I find that hard to believe and cant find any confirmation.
Also...from a design standpoint, I find it odd that GM didnt change the glow plug holes in 2004.5 for the LLY. They knew the glow plugs were going to be completely different, and they changed the thread for 2006...why not 2004.5?? 2004.5-2005 and 2006+ glow plugs are electrically the same (both fast-heat 4.7v)...so why not make 2004.5-2005 and 2006+ glow plugs physically interchangeable?? Having 2001-2004 12v glow plugs and 2004.5-2005 glow plugs physically interchangeable is completely stupid...just asking for problems. Even some parts stores like Autozone and Advance auto parts list 2001-2005 glow plugs as being the same, because they are physically the same...but NOT electrically the same!
Also sucks because 2004.5-2005 glow plugs are unique, and produced in lower numbers...which makes them almost twice as expensive as 2001-2004 and 2006+ glow plugs. But then again, thats par for the course with a lot of 2004.5-2005 LLY parts...shortest engine run = most limited amount of new and used parts available.
To think that, here we are, 15 years later still using the same basic engine design that was put together in 3 months, through all of the emissions changes etc. is pretty incredible, and a strong testament to GM Powertain/Isuzu's competency in engine design.
Couple little incorrect facts in there, but mostly a very good article. LBZ and LMM have the same compression ratio (16.8:1). And Ive never heard of Duramax's breaking camshafts. I think the LMM heads were mostly the same as LBZ, but have some minor differences. Guy would be the one to ask about that.
And then it has obviously not been updated for LML stuff...2011+ LML uses updated block, crank, rods, heads, pistons, fuel system, turbo, and engine controller. Camshaft is the same though as far as I know. I thought I heard somewhere that the LML has a CGI block, but I find that hard to believe and cant find any confirmation.
Also...from a design standpoint, I find it odd that GM didnt change the glow plug holes in 2004.5 for the LLY. They knew the glow plugs were going to be completely different, and they changed the thread for 2006...why not 2004.5?? 2004.5-2005 and 2006+ glow plugs are electrically the same (both fast-heat 4.7v)...so why not make 2004.5-2005 and 2006+ glow plugs physically interchangeable?? Having 2001-2004 12v glow plugs and 2004.5-2005 glow plugs physically interchangeable is completely stupid...just asking for problems. Even some parts stores like Autozone and Advance auto parts list 2001-2005 glow plugs as being the same, because they are physically the same...but NOT electrically the same!
Also sucks because 2004.5-2005 glow plugs are unique, and produced in lower numbers...which makes them almost twice as expensive as 2001-2004 and 2006+ glow plugs. But then again, thats par for the course with a lot of 2004.5-2005 LLY parts...shortest engine run = most limited amount of new and used parts available.
I remember reading that article a while back and thought it was incredibly interesting. Specifically because it covers aspects of the engine that are not mentioned in any of the other dozens of run-of-the-mill "about the duramax" articles. Particularly about the 90-day engine design, and using the time difference to their advantage.
To think that, here we are, 15 years later still using the same basic engine design that was put together in 3 months, through all of the emissions changes etc. is pretty incredible, and a strong testament to GM Powertain/Isuzu's competency in engine design.
Couple little incorrect facts in there, but mostly a very good article. LBZ and LMM have the same compression ratio (16.8:1). And Ive never heard of Duramax's breaking camshafts. I think the LMM heads were mostly the same as LBZ, but have some minor differences. Guy would be the one to ask about that.
And then it has obviously not been updated for LML stuff...2011+ LML uses updated block, crank, rods, heads, pistons, fuel system, turbo, and engine controller. Camshaft is the same though as far as I know. I thought I heard somewhere that the LML has a CGI block, but I find that hard to believe and cant find any confirmation.
Also...from a design standpoint, I find it odd that GM didnt change the glow plug holes in 2004.5 for the LLY. They knew the glow plugs were going to be completely different, and they changed the thread for 2006...why not 2004.5?? 2004.5-2005 and 2006+ glow plugs are electrically the same (both fast-heat 4.7v)...so why not make 2004.5-2005 and 2006+ glow plugs physically interchangeable?? Having 2001-2004 12v glow plugs and 2004.5-2005 glow plugs physically interchangeable is completely stupid...just asking for problems. Even some parts stores like Autozone and Advance auto parts list 2001-2005 glow plugs as being the same, because they are physically the same...but NOT electrically the same!
Also sucks because 2004.5-2005 glow plugs are unique, and produced in lower numbers...which makes them almost twice as expensive as 2001-2004 and 2006+ glow plugs. But then again, thats par for the course with a lot of 2004.5-2005 LLY parts...shortest engine run = most limited amount of new and used parts available.
Funny you mention the lb7 and lly glow plugs being interchangeable but different voltages. I bought a set of garbage diesel rx glow plugs about 2 years ago. They had listed "01-05". So I ordered a set and left a note saying I needed plugs for an lly. Sure enough I get a set of "01-05" glow plugs. I call those idiots and asked them if they realize that lb7 and lly glow plugs are electronically different, lb7 is 12 and lly is fast heat 4.7v?? They tell me there is no difference and the they have sold thousands of sets with no complaints so I said to prove you idiots wrong I'm going to install them and I'll video my truck not being able to start the next morning. He said (with an attitude) if we're wrong I'll refund you your money...as you can imagine, trying to heat 12v plugs on 4.7v doesn't work. He argued with me and said his engineers were not aware of any differences in lb7 vs lly glow plugs and that I shouldn't be having issues. I said give me a refund or send me lly specific plugs. I got a refund:rofl:
Went to the dealer the next day and bought the 4 BERU they had in stock, swapped out the 2 bad original ones and put 2 in my box for spares.
I'm going to bring this one back from the dead. Had somebody arguing with me that the Duramax was all Isuzu, and no way would 2 different engineering divisions work together on one project, so I linked to this article. In searching for it, I found an updated version of this article. A good bit of the info is the same as they used alot of the same sources, but it goes a bit more in depth, and covers some on the L5P.
Despite what you see on the streets, work sites and drag strips of America today, General Motors’ diesel engine hasn’t always been treated with affection by its owners and with respect (even if somewhat reluctantly) by its competitors.
Today’s Duramax engines are recognized as dependable, powerful engines capable of being enhanced by internal engine modifications as well as bolt-on technology. They are used for towing and hauling, frequently over long distances and through unforgiving environments. They are asked to perform at the highest level and be ready to go at it again and again. Like other diesels, they are easily capable of traveling half a million miles – with proper attention and maintenance, of course.
But the 6.6L Duramax found in today’s Chevy Silverados, GMC Sierras, Chevy Express and GMC Savannas (as well as countless other trucks and even cars of a more vintage nature) is a long way from the diesel engines GM tried to bring to market originally.
According to Roy Berndt, engine expert and Engine Builder contributing editor, GM faced an uphill battle to competing in the diesel arena.
“In 1996, as General Motors was finalizing plans for its next generation of full-size trucks (code named GMT800), the company had only 3% market-share of the diesel-powered heavy-duty pick-up truck segment,” says Berndt. “This was really no surprise, since GM had single-handedly alienated the American buying public against the diesel engine beginning back in the late ’70s and early ’80s with the 5.7L V8 and 4.3L V6 diesel engines that were, let’s just say, ‘less than stellar.’ While there’s no point now in rehashing mistakes of the past, the 6.2L and 6.5L diesels had continued on in a similar tradition, even though the 6.5L was used in the HUMVEE for the military.”
The 6.2L and 6.5L diesel engines of the late ’80s were really no match for the Cummins 6BT diesel found in the Dodge Ram in 1989 nor the Ford/International Power Stroke available from Ford in 1999. Partnerships between the other vehicle manufacturers and their engine suppliers had effectively neutered GM’s diesel program and by 1999, GM didn’t even offer a diesel engine in any of its mid-size trucks.
However, behind the scenes, GM and Japanese engine maker Isuzu were working on a joint venture intended to produce a truly modern diesel engine. The collaboration created DMAX Ltd. “The name signified the diesel engine and maximum power, cleanliness and fuel economy,” says Berndt, “and the 13 hour time difference between Japan and the U.S. worked to their advantage.” Teams could videoconference late in the day for one team, early for the other, working on issues while the other team slept.
The new engine that resulted from this joint venture was a 6.6L, 90-degree, direct-injection, overhead valve, four-valve-per-cylinder, turbocharged diesel V8 with aluminum high swirl cylinder heads. An innovative electrically controlled common-rail fuel system provided maximum power for each pulse of fuel used and allowed full authority in injection timing and quantity. This combination along with pilot injection provided operating quietness and smoothness typical of similarly sized gasoline engines.
“When it came time to decide upon the marketing name for the new engine, GM was already handicapped by its poor diesel reputation,” Berndt explains. “The name itself was critical, as it would compete against Ford’s established ‘Power Stroke’ diesel engine. Dodge was using the Cummins engine and needed no other name, so after many meetings the engine was named Duramax Diesel 6600. Like the joint venture name, ‘Duramax’ was meant to highlight the durability and reliability of the new engine.”
In late 2000, the Duramax Diesel 6600 debuted in the new 2001 HD pickup trucks. Brought to market in only 37 months, it was the fastest new engine developed by GM Powertrain to date. The engine was an immediate success, making Ward’s “10 Best Engines” both in 2001 and 2002, and bringing up GM’s market share from 3 percent to 30 percent in the HD Diesel pick-up truck market.
The Duramax Evolution
Since its introduction, there have been multiple generations of the Duramax engine platform, all based on the original 6.6L design. They are all still relevant in the aftermarket.
LB7
The LB7 Duramax was first introduced for the 2001 model year in the Chevrolet Silverado HD, GMC Sierra HD, GMC TopKick (medium duty) and Chevrolet Kodiak (medium duty) trucks. That year also brought the Allison 1000, arguably the first automatic transmission in its class worthy of being mated to a powerful diesel. The LB7 was the pioneer of common rail technology, as Dodge would not introduce its own common rail Cummins until the 2003 model year – Ford wouldn’t add it to the Power Stroke until 2008.
The LB7 is a favorite engine, dramatically different from other Duramax models – it predates emissions regulations. As such, it’s praised for reliability and has been regarded as a particularly economical variation of the engine.
As impressive as GM’s new engine platform appeared, however, the LB7 had terrible problems with fuel injectors failing. In fact, injector failures were so frequent that GM was forced to recall the poorly designed units and replace them with an updated design. In order to provide loyal customers with a sense of reassurance, the factory warranty was extended to cover the new injectors for up to 200,000 miles.
“The integrity of the engine was great,” explains Engine Builder contributor and diesel expert Bob McDonald. “Its biggest problem was the fuel system, and particularly, injector failure. The engine used the Bosch common rail fuel system, which included the high-pressure fuel pump, high-pressure fuel rail, hard lines, injectors and electronic control module. For some reason, the Bosch injectors could not survive in the Duramax and would fail in three different ways – all related to the injector’s body becoming cracked.”
McDonald explains that one symptom of a cracked injector is excessive white smoke coming from the tailpipe, generally most noticeable at idle, especially while sitting in traffic. Fuel is entering the combustion chamber at the wrong time, causing the white smoke, showing an unburned fuel condition.
Fuel leaking into the combustion chamber, cannot be controlled by the engine’s ECU. Known as an injector’s balance rate this can be seen with a scan tool. The balance rates of an injector are adjustments of fuel to the injector made by the ECU, adjustments made from fluctuations of the crankshaft detected by the crankshaft position sensor.
The balance rates are given by the value being a plus or a minus to the volume of fuel per cylinder. If there is too much fuel for a particular cylinder, the balance rates for that cylinder would be a minus. The ECU then tries to take fuel away to correct the imbalance condition. White smoke indicates this minus balance rate caused by a cracked injector.
Another symptom of cracked injector failure is fuel dilution of the engine oil. This is due to an injector’s body being cracked externally, causing fuel to leak into the crankcase.
The injectors of the LB7 were located under the valve cover. The hard lines went from the high-pressure fuel rail and through the valve cover. If the injectors were leaking externally, fuel dilution could happen fairly quickly and go unnoticed because the engine would continue to operate fine.
There have been cases or injectors leaking externally so badly that the crankcase had filled with so much diesel that it began leaking from the rear main seal.
The last form of injector failure was a hot-engine, hard-start condition. When the engine was cold, the vehicle would start fine and drive normally without any noticeable problems – until the owner decided to stop somewhere on the trip.
When the owner would try to restart the vehicle, the engine would spin over but never fire.
This was caused by the injector’s body being cracked on the return side. The heat from the engine would literally cause the crack in the injector body to expand further, causing the fuel pressure that was entering the injector to be returned to the fuel tank.
The vehicle would have to sit for several hours and cool down before the engine would restart.
With so many injector failures between 2001 and 2004, GM extended the injectors’ warranty from five years/100,000 miles to seven years/200,000 miles. This did not, however, remedy the problem.
The biggest problem came when customers had their injectors replaced under the seven-year/200,000-mile warranty. Then several years later, after the truck was out of warranty, the injectors failed again, which, of course angered many customers because there was still a problem and now they were going to have to pay for it. And, if the other injectors didn’t last very long, this would be an ongoing problem for the owner.
With the injectors being under the valve cover, a lot of the components of the top of the engine have to be removed in order to access them so injector replacement in the LB7 Duramax is labor intensive.
It’s always advised that if there are several injectors causing problems that it’s better to replace them all because of the amount of labor that it takes to get to the injector.
The average cost of an injector replacement on the LB7 is generally around $4,000 to $5,000. The replacement process takes between 10 to 12 hours of labor and the injectors cost around $350 each. Bosch went through several designs before there seemed to be a cure.
LLY
In the middle of 2004, GM released the second generation of the Duramax, with the RPO code of LLY, with the eighth digit of the VIN designated as number 2. The LLY was GM’s first attempt to implement emissions requirements on its diesel trucks. To meet this goal GM turned to a newly developed Garrett turbocharger with a variable geometry vane system and installed an Exhaust Gas Recirculation valve. Learning from problems with injectors in the previous LB7, GM changed the valve covers to not only remove them from the engine oiling system, but allow access to the injectors without having to remove the valve covers.
There were several reasons for the change: the injectors changed design and were now on the outside of the valve covers, providing easier access, and the EPA was tightening down on emissions standards for diesel engines in order to reduce NOx gas.
The LLY incorporated the use of an EGR (exhaust gas recirculation) valve. When engine conditions would reach a certain criteria determined by the ECU, the EGR valve would open to reintorduce exhaust gas be reintroduced into the intake manifold.
This often caused a buildup of soot in the intake system because the exhaust gas displacing the oxygen meant cooler combustion; the cooler combustion inside the cylinder formed soot.
In order to reintroduce exhaust gas into the intake of a diesel engine, the exhaust gas has to pass through what is known as an EGR cooler. A diesel engine exhaust temperatures can be much higher than gasoline, reaching as high as 1,200° F.
Before the exhaust gas reenters the intake at this temperature, it has to be cooled. The EGR cooler is more or less a small radiator that is a part of the engine’s cooling system, which as the hot exhaust gas passes through the cooler will cool the exhaust gas before reaching the intake manifold.
Over a period of time, the EGR coolers will fail, causing the engine coolant to enter the intake manifold. This will often result in loss of coolant with steam emitting from the tailpipe.
The LLY suffered from overheating. When Duramax incorporated the use of the EGR cooler, the cooling system of the engine was not upgraded.
When towing with the LLY up steep grades on a hot summer day, owners often noticed that the cooling system could not sustain the engine’s temperature and would overheat.
One of the other features of the LLY was the use of a VNT (variable nozzle turbo). The VNT allowed the turbocharger to change speed by altering exhaust pulses to the turbine wheel. This created better spool time and more boost for the engine off idle and would also change spool at the turbo when the engine was at cruising speed for the use of less boost. This more or less lets the turbo make boost when there is a demand.
The VNT was sometimes responsible for the overheating issues of the LLY because of the more restricted exhaust system. Some overheating issues did result, however, in head gasket failures, which could damage the entire engine.
Early on, problems came forward from customers complaining of severe overheating, and, in some situations, blown head gaskets. Although initially GM denied that it was a problem, after it was sued by a consumer group it relented and included overheating and blown head gaskets as a warranted item.
LBZ
The LBZ was relatively short-lived, available for only two model years for no other reason other than its replacement, the LMM, was introduced with the capability of meeting stricter emissions regulations coming over the horizon. Mechanically, the LBZ is nearly identical to the 2006 model year LLY but features more aggressive engine tuning, producing more horsepower and torque. The LBZ produced 360 horsepower and 650 lb.-ft. of torque to the LLY’s 310 horsepower and 605 lb.-ft.
The block was redesigned with more integrity along with the pistons and rods for the increase in horsepower to 360 and 650 ft.-lbs. of torque. The cooling system was upgraded with the use of a bigger radiator and fan along with a bigger EGR cooler. Under the LBZ, the Bosch fuel engine management system also changed. This time, the fuel system used a new 32-bit controller along with seven hole injectors.
The fuel pressures increased from 23,000 psi to 26,000 psi. Fuel sprayed directly onto the glow plugs for faster starts. The glow plugs were also independently controlled from the use of a controller for more efficiency during cold starts.
The 6.6L Duramax LBZ’s applications included the Chevrolet Silverado HD, GMC Sierra, HD, Chevrolet Kodiak, and GMC TopKick (the Kodiak and TopKick being medium duty truck models. In the aftermarket, the LBZ is thought of the “hot rod” for its huge performance potential, abundance of support, and the fact that it is the last model produced without a diesel particulate filter. Information released by General Motors at the introduction of the LBZ state that the engine has an increased piston pin diameter and thicker connecting rod section over previous generations in addition to an improved block casting.
The block was redesigned with more integrity along with the pistons and rods for the increase in horsepower to 360 and 650 ft.-lbs. of torque. The cooling system was upgraded with the use of a bigger radiator and fan along with a bigger EGR cooler.
The LBZ was available with either the Allison 1000 6-speed automatic or the ZF650 6-speed manual transmission, though 2007 would mark the last model year that any Duramax engine was available with a stick shift. The Allison transmission also changed from 5-speed to a 6-speed. The additional gear in the transmission reduced cruising speed by 200 rpm.
Owners of an earlier LLY were able to upgrade the cooling system of their vehicles by installing the radiator and fan along with the fan shroud from an LBZ. By mid-model year for 2007, the LBZ was effectively replaced by the emissions compliant, diesel particulate filter-equipped LMM.
LMM
From 2007 to 2010, the fourth generation Duramax was known as the LMM. The eighth digit of the VIN is designated with the number 6. RPO LMM engines are based on the LBZ engines, but were designed for U.S. EPA’s 2007 emission standards, and uses ultra-low sulfur diesel fuel, which went on sale in the US and Canada in the fall of 2006.
The LMM makes 365 hp and 660 ft.-lbs. of torque. Because the emissions standards for diesel engines were changing for lower NOx gas, the LMM incorporated the use of a DPF (diesel particulate filter) in the exhaust system.
The DPF is located behind the catalytic converter to trap soot coming from the engine. The DPF is monitored by the engine’s ECU by the use of pressure sensors located in the exhaust system. When the computer senses a pressure differential between two sensors (one located upstream and another downstream of the DPF) the truck enters a “regeneration” cycle. When the DPF becomes clogged with soot, the ECU will actuate the injectors on the exhaust stroke, dumping raw fuel into the DOC (Diesel Oxidizing Catalyst) where it is burned to elevate the temperature of the exhaust. The fuel ignites in the exhaust system, burning away the soot from the filter in the DPF.
This was an effective way to rid soot from the tailpipe, but causes more fuel consumption. In addition, the late and post injection technique poses the threat of cylinder washing and fuel dilution as a result of raw diesel fuel passing through the cylinder on its journey to the exhaust system. The typical response to abnormally high fuel dilution is to make sure that maintenance is performed regularly.
GM reports that this engine and its adopted emissions technologies were able to cut particulate emissions by up to 90 percent over previous generations. The backlash of the DPF system was a severe reduction in fuel economy resulting from periodic regeneration cycles required to clean the particulate filter and prevent clogging.
LML
In 2011, the fifth generation of the Duramax, named the LML, was introduced. The LML is said to have been engineered using 60 percent newly designed components not carried over from a previous generation Duramax. This includes an upgraded engine block casting, oil pump, high strength pistons and connecting rods, main bearing design, and re-routed oil passage circuit. Rated at 397 horsepower and 765 lb.-ft. of torque, the engine is significantly more powerful than any prior Duramax.
The LML was released shortly after Ford’s 390 hp/735 lb.-ft. 6.7L Power Stroke became available, causing Ford to quickly increase the Power Stroke’s available horsepower and torque rating via a free performance upgrade to owners. The upgrade re-calibrated the engine to the tune of 400 horsepower and 800 lb.-ft.
The LML incorporates the use of diesel exhaust fluid injection as an emissions exhaust aftertreatment. Urea is injected downstream of the turbo, which becomes a catalyst for NOx gas. Also, the fuel injection has changed to accommodate the use of piezo injectors and injection pressures reaching 29,000 psi.
Piezo injectors incorporate piezo crystals that are used to create movement of the injector’s pintle, which is faster than the traditional electromagnet.
This, along with the higher injection pressure, further increased engine efficiency.
The LML Duramax’s advanced emissions equipment, including the use of diesel exhaust fluid injection, allowed GM to reduce nitrogen oxide emission levels by 63 percent over LMM powered trucks. This allows the LML to exceed currently mandated federal emissions requirements and potentially meet future requirements as well.
The LML introduced the “9th injector” system in order to supply fuel to the DPF during regeneration. This is opposed to the previous generation’s (LML) late/post injection technique. The result eliminated cylinder washing concerns and permitted the use of up to B20 biodiesel. The implementation of the SCR system, which requires a constant supply of diesel exhaust fluid (DEF), was met with heavy scrutiny. However, this technology actually allows for an advantageous engine calibration to be executed, reducing the duty cycle of DPF regenerations and providing significant improvements in fuel economy. DEF is not particularly costly and owners incur noticeable fuel savings even while factoring in the cost of exhaust fluid. GM’s official statement is that fuel mileage increased 11 percent over the previous generation LMM engine.
LGH
The Duramax LGH is a detuned version of the Duramax LML also introduced for the 2011 model year. It was designed specifically for chassis cab and box-delete vehicles (RPO ZW9), which are considered incomplete vehicles and therefore fall under a different Federal emissions standard category than pickups. The engine doesn’t require the same compliance as the standard LML.
The LGH (VIN code “L”) is used on 2010 interim and 2011 Chevrolet Express and GMC Savana vans and 2011 Chevrolet Silverado and GMC Sierra trucks with RPO ZW9 (chassis cabs or trucks with pickup box delete).
Beginning the 2011 model year, LGH applications included the Chevrolet Silverado 2500/3500 chassis cab, GMC Sierra 2500/3500 chassis cab, Chevrolet Express 3500/4500, and GMC Savana 3500/4500.
In chassis cab applications, the LGH is rated at 335 horsepower and 685 lb.-ft. of torque. For commercial Vans, the LGH is rated at 260 horsepower and 525 lb.-ft. Both power variations retain the LML’s B20 biodiesel compatibility. In addition to a unique engine calibration, the LGH features a different turbocharger, larger EGR cooler, and higher capacity SCR system. Beginning for the 2013 model year, all Sierra and Silverado chassis cab trucks received the more powerful LML instead of the LGH. The transition from the LGH to the LML for the 2013 model year in these applications was likely a strategic move in competing with other brand commercial vehicles.
L5P
The latest generation of Duramax power was introduced this year in the 2017 MY Silverado and Sierra HD pickups. Experts say that while the L5P (VIN Code “Y”) maintains the 6.6L displacement and bore and stroke of its predecessors, it is really more of a “clean sheet” design.
The L5P produces an SAE-certified 910 lb.-ft. of torque and 445 horsepower features an all-new, stronger cylinder block and rotating assembly, as well as a new, GM-developed control system. The engine’s production of low-rpm torque hasn’t changed: the L5P offers 90 percent of peak torque at a low 1,550 rpm and sustains it through 2,850 rpm, an attribute that contributes to the strong, confident pulling power at low speeds of the vehicles in which it powers.
The new L5P features a new camshaft profile and improved cylinder head design; a new electronically controlled, variable-vane turbocharger allows the engine to produce more power with lower exhaust emissions. The engine’s advanced variable-vane mechanism allows greater exhaust temperature capability, enabling the engine to achieve higher power at lower cylinder pressure.
Additionally, a new, patent-pending vehicle air intake system with functional hood scoop drives cool, dry air into the engine for sustained performance and cooler engine temperatures during difficult conditions, such as trailering (towing) on steep grades.
Cooler air helps the engine run better under load, especially in conditions where engine and transmission temperatures can rise quickly. This enbales the Duramax to maintain more power and vehicle speed when trailering in the toughest conditions.
As with previous versions, the new Duramax block features a strong cast-iron foundation known for its durability, with induction-hardened cylinder walls and five nodular iron main bearings. It retains the same 4.05-inch (103mm) and 3.89-inch (99mm) bore and stroke dimensions as the current engine, retaining the Duramax’s familiar 6.6L (403 cu.-in./6,599 cc) displacement.
A deep-skirt design and four-bolt, cross-bolted main caps help ensure the block’s strength and enable more accurate location of the rotating assembly. A die-cast aluminum lower crankcase also strengthens the engine block and serves as the lower engine cover, while reducing its overall weight.
The new engine block incorporates larger-diameter crankshaft connecting rod journals than the current engine, enabling the placement of a stronger crankshaft and increased bearing area to handle higher cylinder loads.
An enhanced oiling circuit, with higher flow capacity and a dedicated feed for the turbocharger, provides increased pressure at the turbo and faster oil delivery. Larger piston-cooling oil jets at the bottom of the cylinder bores spray up to twice the amount of engine oil into oil galleries under the crown of the pistons, contributing to lower engine temperature and greater durability.
A new, two-piece oil pan contributes to the new Duramax’s quieter operation. It consists of a laminated steel oil pan with an upper aluminum section. The aluminum section provides strength-enhancing rigidity for the engine, but a pan made entirely of aluminum would radiate more noise, so the laminated steel lower section is added to dampen noise and vibration.
There’s also an integrated oil cooler with 50 percent greater capacity than the current engine’s, ensuring more consistent temperatures at higher engine loads.
A tough, forged micro-alloy steel crankshaft anchors the new Duramax’s stronger rotating assembly. Cut-then-rolled journal fillets contribute to its durability by strengthening the junction where the journals — the round sections on which the bearings slide — meet the webs that separate the main and rod journals.
The connecting rods are stronger, too, and incorporate a new 45-degree split-angle design to allow the larger-diameter rod bearings to pass through the cylinder bores during engine assembly. They’re forged and sintered with a durable powdered metal alloy, with a fractured-cap design enabling more precise cap-to-rod fitment.
A new, stronger cast aluminum piston design tops off the rotating assembly. It features a taller crown area and a remelted combustion bowl rim for greater strength. Remelting is an additional manufacturing process for aluminum pistons in which the bowl rim area is reheated after casting and pre-machining, creating a much finer and more consistent metal grain structure that greatly enhances thermal fatigue properties.
Additionally, the Duramax’s pistons don’t use pin bushings, reducing reciprocating weight to help the engine rev quicker and respond faster to throttle changes
The redesigned engine retains the Duramax’s signature first-in-class aluminum cylinder head design, with six head bolts per cylinder and four valves per cylinder. The aluminum construction helps reduce the engine’s overall weight, while the six-bolt design provides exceptional head-clamping strength – a must in a high-compression, turbocharged application.
A new aluminum head casting uses a new double-layer water core design that separates and arranges water cores in layers to create a stiffer head structure with more precise coolant flow control. The heads’ airflow passages are also heavily revised to enhance airflow, contributing to the engine’s increased horsepower and torque.
The Duramax employs a common-rail direct injection fuel system with new high-capability solenoid-type injectors. High fuel pressure of 29,000 psi (2,000 bar) promotes excellent fuel atomization for a cleaner burn that promotes reduced particulate emissions. The new injectors also support up to seven fuel delivery events per combustion event, contributing to lower noise, greater efficiency, and lower emissions. Technology advancements enable less-complex solenoid injectors to deliver comparable performance to piezo-type injectors.
Turbocharging System
A new electronically controlled, variable-vane turbocharger advances the Duramax’s legacy of variable-geometry boosting. Compared to the current engine, the system produces higher maximum boost pressure – 28 psi – to help the engine make more power, and revisions to enhance the capability of the exhaust-brake system.
Along with a new camshaft profile and improved cylinder head design, the Duramax’s new variable-vane turbocharger enables the engine to deliver more power with lower exhaust emissions. It uses a more advanced variable vane mechanism, allowing a 104-degree F (40 C) increase in exhaust temperature capability. The self-contained mechanism decouples movement from the turbine housing, allowing operation at higher temperature. That enables the engine to achieve higher power at lower cylinder pressure. Additionally, it has lower internal leakage, allowing more exhaust energy to be captured during exhaust braking.
The integrated exhaust brake system makes trailering less stressful by creating additional backpressure in the exhaust, resulting in negative torque during deceleration and downhill driving, enhancing driver control and prolonging brake pad life.
A new venturi jet drain oil separator used with the Duramax 6.6L is the first of its type in the segment and is designed to ensure oil control in sustained full-load operation. The totally sealed system collects the fine mist of oil entrained in the blow-by gas and uses a small portion of the boosted air generated by the turbocharger to pump the collected oil back to the engine oil sump for re-use by the engine. GM says less-sophisticated systems are not able to return this oil during full-load operation, which can result in oil carryover into the cylinders during combustion.
The new Duramax also provides outstanding cold-weather performance, with microprocessor-controlled glow plugs capable of gas-engine-like starting performance in fewer than three seconds in temperatures as low as -20degrees F (-29 C), without a block heater. The system is enhanced with ceramic glow plugs and automatic temperature compensation – a first-in-class feature providing improved robustness and capability. The automatic temperature compensation assesses and adjusts the current to each glow plug for every use, providing optimal temperature for cold start performance and durability.
Unlike a gasoline engine, a diesel engine doesn’t necessarily require a throttle control system. The Duramax 6.6L employs an electronic throttle valve to regulate intake manifold pressure in order to increase exhaust gas recirculation (EGR) rates. It also contributes to smoother engine shutdown.
Additionally, a cooled exhaust gas recirculation (EGR) system enhances performance and helps reduce emissions by diverting some of the engine-out exhaust gas and mixing it back into the fresh intake air stream, which is fed through the cylinder head for combustion. This lowers combustion temperatures, improving emissions performance by reducing NOx formation.
The exhaust is cooled in a unique heat exchanger before it’s fed into the intake stream through a patented EGR mixing device, further improving emissions and performance capability. An integrated bypass allows non-cooled exhaust gas to be fed back into the system to help the engine more quickly achieve optimal operating temperature when cold.
The new Duramax 6.6L is capable of running on B20 biodiesel, a fuel composed of 20 percent biodiesel and 80 percent conventional diesel. B20 helps lower carbon dioxide emissions and lessens dependence on petroleum. It is a domestically produced, renewable fuel made primarily of plant matter – mostly soybean oil.
There are literally hundreds of products available to complement Duramax engines of every vintage. From internal components such as connecting rods, roller rocker systems, pistons, head gaskets, injectors and lift pumps to bolt-on accessories such as air intakes and filters, electronics and exhaust systems, your suppliers can hook you and your customers up with the goods.
GM may have stumbled out of the blocks but success in the diesel market is a marathon, not a s print – and the General is definitely still in the race. ν
Much thanks goes to Engine Builder contributors Roy Berndt, Ron Knoch and Bob McDonald for their invaluable research for this article. Other resources include General Motors, gmauthority.com, and duramaxhub.com. For more information on our coverage of diesel engines in general and the 6.6L Duramax in particular, visit www.enginebuildermag.com.
Despite what you see on the streets, work sites and drag strips of America today, General Motors’ diesel engine hasn’t always been treated with affection by its owners and with respect (even if somewhat reluctantly) by its competitors.
Today’s Duramax engines are recognized as dependable, powerful engines capable of being enhanced by internal engine modifications as well as bolt-on technology. They are used for towing and hauling, frequently over long distances and through unforgiving environments. They are asked to perform at the highest level and be ready to go at it again and again. Like other diesels, they are easily capable of traveling half a million miles – with proper attention and maintenance, of course.
But the 6.6L Duramax found in today’s Chevy Silverados, GMC Sierras, Chevy Express and GMC Savannas (as well as countless other trucks and even cars of a more vintage nature) is a long way from the diesel engines GM tried to bring to market originally.
According to Roy Berndt, engine expert and Engine Builder contributing editor, GM faced an uphill battle to competing in the diesel arena.
“In 1996, as General Motors was finalizing plans for its next generation of full-size trucks (code named GMT800), the company had only 3% market-share of the diesel-powered heavy-duty pick-up truck segment,” says Berndt. “This was really no surprise, since GM had single-handedly alienated the American buying public against the diesel engine beginning back in the late ’70s and early ’80s with the 5.7L V8 and 4.3L V6 diesel engines that were, let’s just say, ‘less than stellar.’ While there’s no point now in rehashing mistakes of the past, the 6.2L and 6.5L diesels had continued on in a similar tradition, even though the 6.5L was used in the HUMVEE for the military.”
The 6.2L and 6.5L diesel engines of the late ’80s were really no match for the Cummins 6BT diesel found in the Dodge Ram in 1989 nor the Ford/International Power Stroke available from Ford in 1999. Partnerships between the other vehicle manufacturers and their engine suppliers had effectively neutered GM’s diesel program and by 1999, GM didn’t even offer a diesel engine in any of its mid-size trucks.
However, behind the scenes, GM and Japanese engine maker Isuzu were working on a joint venture intended to produce a truly modern diesel engine. The collaboration created DMAX Ltd. “The name signified the diesel engine and maximum power, cleanliness and fuel economy,” says Berndt, “and the 13 hour time difference between Japan and the U.S. worked to their advantage.” Teams could videoconference late in the day for one team, early for the other, working on issues while the other team slept.
The new engine that resulted from this joint venture was a 6.6L, 90-degree, direct-injection, overhead valve, four-valve-per-cylinder, turbocharged diesel V8 with aluminum high swirl cylinder heads. An innovative electrically controlled common-rail fuel system provided maximum power for each pulse of fuel used and allowed full authority in injection timing and quantity. This combination along with pilot injection provided operating quietness and smoothness typical of similarly sized gasoline engines.
“When it came time to decide upon the marketing name for the new engine, GM was already handicapped by its poor diesel reputation,” Berndt explains. “The name itself was critical, as it would compete against Ford’s established ‘Power Stroke’ diesel engine. Dodge was using the Cummins engine and needed no other name, so after many meetings the engine was named Duramax Diesel 6600. Like the joint venture name, ‘Duramax’ was meant to highlight the durability and reliability of the new engine.”
In late 2000, the Duramax Diesel 6600 debuted in the new 2001 HD pickup trucks. Brought to market in only 37 months, it was the fastest new engine developed by GM Powertrain to date. The engine was an immediate success, making Ward’s “10 Best Engines” both in 2001 and 2002, and bringing up GM’s market share from 3 percent to 30 percent in the HD Diesel pick-up truck market.
The Duramax Evolution
Since its introduction, there have been multiple generations of the Duramax engine platform, all based on the original 6.6L design. They are all still relevant in the aftermarket.
LB7
The LB7 Duramax was first introduced for the 2001 model year in the Chevrolet Silverado HD, GMC Sierra HD, GMC TopKick (medium duty) and Chevrolet Kodiak (medium duty) trucks. That year also brought the Allison 1000, arguably the first automatic transmission in its class worthy of being mated to a powerful diesel. The LB7 was the pioneer of common rail technology, as Dodge would not introduce its own common rail Cummins until the 2003 model year – Ford wouldn’t add it to the Power Stroke until 2008.
The LB7 is a favorite engine, dramatically different from other Duramax models – it predates emissions regulations. As such, it’s praised for reliability and has been regarded as a particularly economical variation of the engine.
As impressive as GM’s new engine platform appeared, however, the LB7 had terrible problems with fuel injectors failing. In fact, injector failures were so frequent that GM was forced to recall the poorly designed units and replace them with an updated design. In order to provide loyal customers with a sense of reassurance, the factory warranty was extended to cover the new injectors for up to 200,000 miles.
“The integrity of the engine was great,” explains Engine Builder contributor and diesel expert Bob McDonald. “Its biggest problem was the fuel system, and particularly, injector failure. The engine used the Bosch common rail fuel system, which included the high-pressure fuel pump, high-pressure fuel rail, hard lines, injectors and electronic control module. For some reason, the Bosch injectors could not survive in the Duramax and would fail in three different ways – all related to the injector’s body becoming cracked.”
McDonald explains that one symptom of a cracked injector is excessive white smoke coming from the tailpipe, generally most noticeable at idle, especially while sitting in traffic. Fuel is entering the combustion chamber at the wrong time, causing the white smoke, showing an unburned fuel condition.
Fuel leaking into the combustion chamber, cannot be controlled by the engine’s ECU. Known as an injector’s balance rate this can be seen with a scan tool. The balance rates of an injector are adjustments of fuel to the injector made by the ECU, adjustments made from fluctuations of the crankshaft detected by the crankshaft position sensor.
The balance rates are given by the value being a plus or a minus to the volume of fuel per cylinder. If there is too much fuel for a particular cylinder, the balance rates for that cylinder would be a minus. The ECU then tries to take fuel away to correct the imbalance condition. White smoke indicates this minus balance rate caused by a cracked injector.
Another symptom of cracked injector failure is fuel dilution of the engine oil. This is due to an injector’s body being cracked externally, causing fuel to leak into the crankcase.
The injectors of the LB7 were located under the valve cover. The hard lines went from the high-pressure fuel rail and through the valve cover. If the injectors were leaking externally, fuel dilution could happen fairly quickly and go unnoticed because the engine would continue to operate fine.
There have been cases or injectors leaking externally so badly that the crankcase had filled with so much diesel that it began leaking from the rear main seal.
The last form of injector failure was a hot-engine, hard-start condition. When the engine was cold, the vehicle would start fine and drive normally without any noticeable problems – until the owner decided to stop somewhere on the trip.
When the owner would try to restart the vehicle, the engine would spin over but never fire.
This was caused by the injector’s body being cracked on the return side. The heat from the engine would literally cause the crack in the injector body to expand further, causing the fuel pressure that was entering the injector to be returned to the fuel tank.
The vehicle would have to sit for several hours and cool down before the engine would restart.
With so many injector failures between 2001 and 2004, GM extended the injectors’ warranty from five years/100,000 miles to seven years/200,000 miles. This did not, however, remedy the problem.
The biggest problem came when customers had their injectors replaced under the seven-year/200,000-mile warranty. Then several years later, after the truck was out of warranty, the injectors failed again, which, of course angered many customers because there was still a problem and now they were going to have to pay for it. And, if the other injectors didn’t last very long, this would be an ongoing problem for the owner.
With the injectors being under the valve cover, a lot of the components of the top of the engine have to be removed in order to access them so injector replacement in the LB7 Duramax is labor intensive.
It’s always advised that if there are several injectors causing problems that it’s better to replace them all because of the amount of labor that it takes to get to the injector.
The average cost of an injector replacement on the LB7 is generally around $4,000 to $5,000. The replacement process takes between 10 to 12 hours of labor and the injectors cost around $350 each. Bosch went through several designs before there seemed to be a cure.
LLY
In the middle of 2004, GM released the second generation of the Duramax, with the RPO code of LLY, with the eighth digit of the VIN designated as number 2. The LLY was GM’s first attempt to implement emissions requirements on its diesel trucks. To meet this goal GM turned to a newly developed Garrett turbocharger with a variable geometry vane system and installed an Exhaust Gas Recirculation valve. Learning from problems with injectors in the previous LB7, GM changed the valve covers to not only remove them from the engine oiling system, but allow access to the injectors without having to remove the valve covers.
There were several reasons for the change: the injectors changed design and were now on the outside of the valve covers, providing easier access, and the EPA was tightening down on emissions standards for diesel engines in order to reduce NOx gas.
The LLY incorporated the use of an EGR (exhaust gas recirculation) valve. When engine conditions would reach a certain criteria determined by the ECU, the EGR valve would open to reintorduce exhaust gas be reintroduced into the intake manifold.
This often caused a buildup of soot in the intake system because the exhaust gas displacing the oxygen meant cooler combustion; the cooler combustion inside the cylinder formed soot.
In order to reintroduce exhaust gas into the intake of a diesel engine, the exhaust gas has to pass through what is known as an EGR cooler. A diesel engine exhaust temperatures can be much higher than gasoline, reaching as high as 1,200° F.
Before the exhaust gas reenters the intake at this temperature, it has to be cooled. The EGR cooler is more or less a small radiator that is a part of the engine’s cooling system, which as the hot exhaust gas passes through the cooler will cool the exhaust gas before reaching the intake manifold.
Over a period of time, the EGR coolers will fail, causing the engine coolant to enter the intake manifold. This will often result in loss of coolant with steam emitting from the tailpipe.
The LLY suffered from overheating. When Duramax incorporated the use of the EGR cooler, the cooling system of the engine was not upgraded.
When towing with the LLY up steep grades on a hot summer day, owners often noticed that the cooling system could not sustain the engine’s temperature and would overheat.
One of the other features of the LLY was the use of a VNT (variable nozzle turbo). The VNT allowed the turbocharger to change speed by altering exhaust pulses to the turbine wheel. This created better spool time and more boost for the engine off idle and would also change spool at the turbo when the engine was at cruising speed for the use of less boost. This more or less lets the turbo make boost when there is a demand.
The VNT was sometimes responsible for the overheating issues of the LLY because of the more restricted exhaust system. Some overheating issues did result, however, in head gasket failures, which could damage the entire engine.
Early on, problems came forward from customers complaining of severe overheating, and, in some situations, blown head gaskets. Although initially GM denied that it was a problem, after it was sued by a consumer group it relented and included overheating and blown head gaskets as a warranted item.
LBZ
The LBZ was relatively short-lived, available for only two model years for no other reason other than its replacement, the LMM, was introduced with the capability of meeting stricter emissions regulations coming over the horizon. Mechanically, the LBZ is nearly identical to the 2006 model year LLY but features more aggressive engine tuning, producing more horsepower and torque. The LBZ produced 360 horsepower and 650 lb.-ft. of torque to the LLY’s 310 horsepower and 605 lb.-ft.
The block was redesigned with more integrity along with the pistons and rods for the increase in horsepower to 360 and 650 ft.-lbs. of torque. The cooling system was upgraded with the use of a bigger radiator and fan along with a bigger EGR cooler. Under the LBZ, the Bosch fuel engine management system also changed. This time, the fuel system used a new 32-bit controller along with seven hole injectors.
The fuel pressures increased from 23,000 psi to 26,000 psi. Fuel sprayed directly onto the glow plugs for faster starts. The glow plugs were also independently controlled from the use of a controller for more efficiency during cold starts.
The 6.6L Duramax LBZ’s applications included the Chevrolet Silverado HD, GMC Sierra, HD, Chevrolet Kodiak, and GMC TopKick (the Kodiak and TopKick being medium duty truck models. In the aftermarket, the LBZ is thought of the “hot rod” for its huge performance potential, abundance of support, and the fact that it is the last model produced without a diesel particulate filter. Information released by General Motors at the introduction of the LBZ state that the engine has an increased piston pin diameter and thicker connecting rod section over previous generations in addition to an improved block casting.
The block was redesigned with more integrity along with the pistons and rods for the increase in horsepower to 360 and 650 ft.-lbs. of torque. The cooling system was upgraded with the use of a bigger radiator and fan along with a bigger EGR cooler.
The LBZ was available with either the Allison 1000 6-speed automatic or the ZF650 6-speed manual transmission, though 2007 would mark the last model year that any Duramax engine was available with a stick shift. The Allison transmission also changed from 5-speed to a 6-speed. The additional gear in the transmission reduced cruising speed by 200 rpm.
Owners of an earlier LLY were able to upgrade the cooling system of their vehicles by installing the radiator and fan along with the fan shroud from an LBZ. By mid-model year for 2007, the LBZ was effectively replaced by the emissions compliant, diesel particulate filter-equipped LMM.
LMM
From 2007 to 2010, the fourth generation Duramax was known as the LMM. The eighth digit of the VIN is designated with the number 6. RPO LMM engines are based on the LBZ engines, but were designed for U.S. EPA’s 2007 emission standards, and uses ultra-low sulfur diesel fuel, which went on sale in the US and Canada in the fall of 2006.
The LMM makes 365 hp and 660 ft.-lbs. of torque. Because the emissions standards for diesel engines were changing for lower NOx gas, the LMM incorporated the use of a DPF (diesel particulate filter) in the exhaust system.
The DPF is located behind the catalytic converter to trap soot coming from the engine. The DPF is monitored by the engine’s ECU by the use of pressure sensors located in the exhaust system. When the computer senses a pressure differential between two sensors (one located upstream and another downstream of the DPF) the truck enters a “regeneration” cycle. When the DPF becomes clogged with soot, the ECU will actuate the injectors on the exhaust stroke, dumping raw fuel into the DOC (Diesel Oxidizing Catalyst) where it is burned to elevate the temperature of the exhaust. The fuel ignites in the exhaust system, burning away the soot from the filter in the DPF.
This was an effective way to rid soot from the tailpipe, but causes more fuel consumption. In addition, the late and post injection technique poses the threat of cylinder washing and fuel dilution as a result of raw diesel fuel passing through the cylinder on its journey to the exhaust system. The typical response to abnormally high fuel dilution is to make sure that maintenance is performed regularly.
GM reports that this engine and its adopted emissions technologies were able to cut particulate emissions by up to 90 percent over previous generations. The backlash of the DPF system was a severe reduction in fuel economy resulting from periodic regeneration cycles required to clean the particulate filter and prevent clogging.
LML
In 2011, the fifth generation of the Duramax, named the LML, was introduced. The LML is said to have been engineered using 60 percent newly designed components not carried over from a previous generation Duramax. This includes an upgraded engine block casting, oil pump, high strength pistons and connecting rods, main bearing design, and re-routed oil passage circuit. Rated at 397 horsepower and 765 lb.-ft. of torque, the engine is significantly more powerful than any prior Duramax.
The LML was released shortly after Ford’s 390 hp/735 lb.-ft. 6.7L Power Stroke became available, causing Ford to quickly increase the Power Stroke’s available horsepower and torque rating via a free performance upgrade to owners. The upgrade re-calibrated the engine to the tune of 400 horsepower and 800 lb.-ft.
The LML incorporates the use of diesel exhaust fluid injection as an emissions exhaust aftertreatment. Urea is injected downstream of the turbo, which becomes a catalyst for NOx gas. Also, the fuel injection has changed to accommodate the use of piezo injectors and injection pressures reaching 29,000 psi.
Piezo injectors incorporate piezo crystals that are used to create movement of the injector’s pintle, which is faster than the traditional electromagnet.
This, along with the higher injection pressure, further increased engine efficiency.
The LML Duramax’s advanced emissions equipment, including the use of diesel exhaust fluid injection, allowed GM to reduce nitrogen oxide emission levels by 63 percent over LMM powered trucks. This allows the LML to exceed currently mandated federal emissions requirements and potentially meet future requirements as well.
The LML introduced the “9th injector” system in order to supply fuel to the DPF during regeneration. This is opposed to the previous generation’s (LML) late/post injection technique. The result eliminated cylinder washing concerns and permitted the use of up to B20 biodiesel. The implementation of the SCR system, which requires a constant supply of diesel exhaust fluid (DEF), was met with heavy scrutiny. However, this technology actually allows for an advantageous engine calibration to be executed, reducing the duty cycle of DPF regenerations and providing significant improvements in fuel economy. DEF is not particularly costly and owners incur noticeable fuel savings even while factoring in the cost of exhaust fluid. GM’s official statement is that fuel mileage increased 11 percent over the previous generation LMM engine.
LGH
The Duramax LGH is a detuned version of the Duramax LML also introduced for the 2011 model year. It was designed specifically for chassis cab and box-delete vehicles (RPO ZW9), which are considered incomplete vehicles and therefore fall under a different Federal emissions standard category than pickups. The engine doesn’t require the same compliance as the standard LML.
The LGH (VIN code “L”) is used on 2010 interim and 2011 Chevrolet Express and GMC Savana vans and 2011 Chevrolet Silverado and GMC Sierra trucks with RPO ZW9 (chassis cabs or trucks with pickup box delete).
Beginning the 2011 model year, LGH applications included the Chevrolet Silverado 2500/3500 chassis cab, GMC Sierra 2500/3500 chassis cab, Chevrolet Express 3500/4500, and GMC Savana 3500/4500.
In chassis cab applications, the LGH is rated at 335 horsepower and 685 lb.-ft. of torque. For commercial Vans, the LGH is rated at 260 horsepower and 525 lb.-ft. Both power variations retain the LML’s B20 biodiesel compatibility. In addition to a unique engine calibration, the LGH features a different turbocharger, larger EGR cooler, and higher capacity SCR system. Beginning for the 2013 model year, all Sierra and Silverado chassis cab trucks received the more powerful LML instead of the LGH. The transition from the LGH to the LML for the 2013 model year in these applications was likely a strategic move in competing with other brand commercial vehicles.
L5P
The latest generation of Duramax power was introduced this year in the 2017 MY Silverado and Sierra HD pickups. Experts say that while the L5P (VIN Code “Y”) maintains the 6.6L displacement and bore and stroke of its predecessors, it is really more of a “clean sheet” design.
The L5P produces an SAE-certified 910 lb.-ft. of torque and 445 horsepower features an all-new, stronger cylinder block and rotating assembly, as well as a new, GM-developed control system. The engine’s production of low-rpm torque hasn’t changed: the L5P offers 90 percent of peak torque at a low 1,550 rpm and sustains it through 2,850 rpm, an attribute that contributes to the strong, confident pulling power at low speeds of the vehicles in which it powers.
The new L5P features a new camshaft profile and improved cylinder head design; a new electronically controlled, variable-vane turbocharger allows the engine to produce more power with lower exhaust emissions. The engine’s advanced variable-vane mechanism allows greater exhaust temperature capability, enabling the engine to achieve higher power at lower cylinder pressure.
Additionally, a new, patent-pending vehicle air intake system with functional hood scoop drives cool, dry air into the engine for sustained performance and cooler engine temperatures during difficult conditions, such as trailering (towing) on steep grades.
Cooler air helps the engine run better under load, especially in conditions where engine and transmission temperatures can rise quickly. This enbales the Duramax to maintain more power and vehicle speed when trailering in the toughest conditions.
As with previous versions, the new Duramax block features a strong cast-iron foundation known for its durability, with induction-hardened cylinder walls and five nodular iron main bearings. It retains the same 4.05-inch (103mm) and 3.89-inch (99mm) bore and stroke dimensions as the current engine, retaining the Duramax’s familiar 6.6L (403 cu.-in./6,599 cc) displacement.
A deep-skirt design and four-bolt, cross-bolted main caps help ensure the block’s strength and enable more accurate location of the rotating assembly. A die-cast aluminum lower crankcase also strengthens the engine block and serves as the lower engine cover, while reducing its overall weight.
The new engine block incorporates larger-diameter crankshaft connecting rod journals than the current engine, enabling the placement of a stronger crankshaft and increased bearing area to handle higher cylinder loads.
An enhanced oiling circuit, with higher flow capacity and a dedicated feed for the turbocharger, provides increased pressure at the turbo and faster oil delivery. Larger piston-cooling oil jets at the bottom of the cylinder bores spray up to twice the amount of engine oil into oil galleries under the crown of the pistons, contributing to lower engine temperature and greater durability.
A new, two-piece oil pan contributes to the new Duramax’s quieter operation. It consists of a laminated steel oil pan with an upper aluminum section. The aluminum section provides strength-enhancing rigidity for the engine, but a pan made entirely of aluminum would radiate more noise, so the laminated steel lower section is added to dampen noise and vibration.
There’s also an integrated oil cooler with 50 percent greater capacity than the current engine’s, ensuring more consistent temperatures at higher engine loads.
A tough, forged micro-alloy steel crankshaft anchors the new Duramax’s stronger rotating assembly. Cut-then-rolled journal fillets contribute to its durability by strengthening the junction where the journals — the round sections on which the bearings slide — meet the webs that separate the main and rod journals.
The connecting rods are stronger, too, and incorporate a new 45-degree split-angle design to allow the larger-diameter rod bearings to pass through the cylinder bores during engine assembly. They’re forged and sintered with a durable powdered metal alloy, with a fractured-cap design enabling more precise cap-to-rod fitment.
A new, stronger cast aluminum piston design tops off the rotating assembly. It features a taller crown area and a remelted combustion bowl rim for greater strength. Remelting is an additional manufacturing process for aluminum pistons in which the bowl rim area is reheated after casting and pre-machining, creating a much finer and more consistent metal grain structure that greatly enhances thermal fatigue properties.
Additionally, the Duramax’s pistons don’t use pin bushings, reducing reciprocating weight to help the engine rev quicker and respond faster to throttle changes
The redesigned engine retains the Duramax’s signature first-in-class aluminum cylinder head design, with six head bolts per cylinder and four valves per cylinder. The aluminum construction helps reduce the engine’s overall weight, while the six-bolt design provides exceptional head-clamping strength – a must in a high-compression, turbocharged application.
A new aluminum head casting uses a new double-layer water core design that separates and arranges water cores in layers to create a stiffer head structure with more precise coolant flow control. The heads’ airflow passages are also heavily revised to enhance airflow, contributing to the engine’s increased horsepower and torque.
The Duramax employs a common-rail direct injection fuel system with new high-capability solenoid-type injectors. High fuel pressure of 29,000 psi (2,000 bar) promotes excellent fuel atomization for a cleaner burn that promotes reduced particulate emissions. The new injectors also support up to seven fuel delivery events per combustion event, contributing to lower noise, greater efficiency, and lower emissions. Technology advancements enable less-complex solenoid injectors to deliver comparable performance to piezo-type injectors.
Turbocharging System
A new electronically controlled, variable-vane turbocharger advances the Duramax’s legacy of variable-geometry boosting. Compared to the current engine, the system produces higher maximum boost pressure – 28 psi – to help the engine make more power, and revisions to enhance the capability of the exhaust-brake system.
Along with a new camshaft profile and improved cylinder head design, the Duramax’s new variable-vane turbocharger enables the engine to deliver more power with lower exhaust emissions. It uses a more advanced variable vane mechanism, allowing a 104-degree F (40 C) increase in exhaust temperature capability. The self-contained mechanism decouples movement from the turbine housing, allowing operation at higher temperature. That enables the engine to achieve higher power at lower cylinder pressure. Additionally, it has lower internal leakage, allowing more exhaust energy to be captured during exhaust braking.
The integrated exhaust brake system makes trailering less stressful by creating additional backpressure in the exhaust, resulting in negative torque during deceleration and downhill driving, enhancing driver control and prolonging brake pad life.
A new venturi jet drain oil separator used with the Duramax 6.6L is the first of its type in the segment and is designed to ensure oil control in sustained full-load operation. The totally sealed system collects the fine mist of oil entrained in the blow-by gas and uses a small portion of the boosted air generated by the turbocharger to pump the collected oil back to the engine oil sump for re-use by the engine. GM says less-sophisticated systems are not able to return this oil during full-load operation, which can result in oil carryover into the cylinders during combustion.
The new Duramax also provides outstanding cold-weather performance, with microprocessor-controlled glow plugs capable of gas-engine-like starting performance in fewer than three seconds in temperatures as low as -20degrees F (-29 C), without a block heater. The system is enhanced with ceramic glow plugs and automatic temperature compensation – a first-in-class feature providing improved robustness and capability. The automatic temperature compensation assesses and adjusts the current to each glow plug for every use, providing optimal temperature for cold start performance and durability.
Unlike a gasoline engine, a diesel engine doesn’t necessarily require a throttle control system. The Duramax 6.6L employs an electronic throttle valve to regulate intake manifold pressure in order to increase exhaust gas recirculation (EGR) rates. It also contributes to smoother engine shutdown.
Additionally, a cooled exhaust gas recirculation (EGR) system enhances performance and helps reduce emissions by diverting some of the engine-out exhaust gas and mixing it back into the fresh intake air stream, which is fed through the cylinder head for combustion. This lowers combustion temperatures, improving emissions performance by reducing NOx formation.
The exhaust is cooled in a unique heat exchanger before it’s fed into the intake stream through a patented EGR mixing device, further improving emissions and performance capability. An integrated bypass allows non-cooled exhaust gas to be fed back into the system to help the engine more quickly achieve optimal operating temperature when cold.
The new Duramax 6.6L is capable of running on B20 biodiesel, a fuel composed of 20 percent biodiesel and 80 percent conventional diesel. B20 helps lower carbon dioxide emissions and lessens dependence on petroleum. It is a domestically produced, renewable fuel made primarily of plant matter – mostly soybean oil.
There are literally hundreds of products available to complement Duramax engines of every vintage. From internal components such as connecting rods, roller rocker systems, pistons, head gaskets, injectors and lift pumps to bolt-on accessories such as air intakes and filters, electronics and exhaust systems, your suppliers can hook you and your customers up with the goods.
GM may have stumbled out of the blocks but success in the diesel market is a marathon, not a s print – and the General is definitely still in the race. ν
Much thanks goes to Engine Builder contributors Roy Berndt, Ron Knoch and Bob McDonald for their invaluable research for this article. Other resources include General Motors, gmauthority.com, and duramaxhub.com. For more information on our coverage of diesel engines in general and the 6.6L Duramax in particular, visit www.enginebuildermag.com.
