See lots of new guys on here with a lot of the same questions so I figured I'd post some stuff on turbos.
First off, I'm not a turbo expert, I have a lot of knowledge on the concept of turbos (studied jet engine design as my major, same idea as turbos) and I have been playing around with turbo trucks for 8 years now. SOOO I can answer how does this work, NOT which turbo should I get for my setup etc.
There is way too much info here lol.
What is a turbo and how does it work?
Ok so here is the basic idea behind the turbo, the compressor does work on the ambient air forcing more air into a set space (your 6.6L engine). This way when your turbo is spooled up its like having a much bigger engine displacement. Now, you cant have something for free so you need to power this compressor. A supercharger is hooked directly to the engine and uses the engine as power. The downside to this is you are taking a lot of the power the engine is making and running the supercharger and not putting it to the ground. A turbo has a turbine that is in the exhaust flow that powers the compressor. While it does rob the engine of some performance in the form of backpressure in the exhaust, its not nearly the same amount as a supercharger. The downside of a turbo is lag, since a supercharger is hooked to the engine mechanically it revs the same as the engine, where the turbo needs the engine to rev, make more exhaust then spool up.
Thermodynamics 101
Ok there is a few principals you need to know to fully understand what goes on. First off, heat in energy. If you do work on air you are energizing it and total temperature will go up, even in a perfect machine. Same thing when you make air do work for you, the total temp will drop. So even if you made a perfect compressor, the total temp of the air is going to go up depending on how much work you do to it. And on the turbine side, the temp is going to drop depending on how much work you are making the air do. If you put a EGT probe on both sides of the turbine, the would read very close to the same when you were not making boost, but on a stock truck it would be about a 300* drop at full boost.
One more thing, the baseline for the atmosphere is approximately 14PSI at sea level, so when your gauge says 0 PSI its really 14PSI total, it is saying there is 0PSI difference from your setup and the atmospheric pressure.
What is a wastegate and why do VVTs not have one?
A wastegate is just that, a valve that opens up to allow extra exhaust to bypass the turbine therefore providing less power to the compressor to prevent the turbo from over boosting/over speeding. A traditional turbo has vanes that guide the exhaust to the turbine to spin it like a pinwheel. A Variable Vane Turbo has vanes that can move, they close down at lower power settings to build more back pressure (and temperature at lower power settings) spooling the turbo quicker. Then as more exhaust is made they open up, and keep the backpressure at such a point to prevent over boosting. The exhaust flowing over the variable vanes is what makes VVTs whistle like they do.
Why do I have a my boost tubes going to this big radiator on the front of my truck? (its called a CAC)
Like I said before, when you do work on air (pressurize it) you create heat. You want the air entering your engine to be as cold as possible. Power is made from the change of the energy state within the cylinder driving the piston down by burring fuel, which creates a lot of heat. Your engine can only take some much heat before you cause parts to fail. So to make more power, you either make the output hotter, or the input colder so you can have a bigger rate of change (there’s some more thermo 101 for you!) so your CAC reduces the total energy of the air going into the engine, while still keeping the amount of air going in, just cooler. That way you can add more fuel and keep the total temp down.
How do I make my turbo make the most amount of boost possible?
Take one of your boost tubes off and either crush it or fill it full of something. Remember, its not PSI alone that you want, its total airflow, so PSI with the only resistance coming from the engine itself. Turbos are designed to work within a certain range of change is pressure (delta P) and airflow (called a MAP). If you take a turbo outside of its MAP your not really going to get much more airflow, but you will do a lot more work on the air in the form of total temp rise, not good. Now you can push your stock turbo a little more than factory, but not much more you are just overspeeding your turbo and making heat with very little airflow gain.
What is a turbo fart/ strange sound when I go from wide open to idle fast?
At WOT you are making a lot of exhaust and your engine is using a lot of air. When you let off fast you take away that exhaust and the need for the airflow causing a spike in the boost PSI (like shutting a door on the intake). With the drop in exhaust the turbine cannot provide enough power to keep the compressor turning, and the compressor stalls and allows the air to flow backwards out the intake. In extreme cases it can even turn the compressor into a turbine and spin the turbo backwards. Not really good for the turbo. To prevent it just let out of the throttle slowly if you can help it so everything has time to react.
Twins compounds and triples
First off two terms: sequential and parallel. Sequential is one turbo feeding another one, so one will pull air in from the atmosphere and the output feeds the input on the next turbo. Parallel both turbos are pulling air from the atmosphere and dumping it together to the engine, one does not feed the other. Every twin gasser I know if is parallel. Most of the diesel “twins” are really sequential setups. Just as a single turbo crams more air into a set space (6.6L) a sequential setup as a turbo cramming more air into the intake of the second turbo. Think of it as the most awesome air intake ever. Now a turbo MAP only cares about how much the CHANGE in pressure over the compressor is. So if the pressure at the intake of the turbo is 100 PSI and the output is 130 PSI, it is exactly the same to the turbo as if it was 0 PSI at the intake and the output was 30PSI. (but the boot holding the output tube on would care!!!) That is why you can get so much boost out of a sequential setup.
The benefit of a sequential setup over a big single is you still have the primary turbo that is small, and will spool quicker and much smother. The downside is all the extra piping that goes with it.
Now for the new cool thing, triples.
In a sequential set up, the atmospheric turbo (the first one the air sees) has to be big, if you are running 28PSI off this first turbo then your compression ratio is 3 (atmospheric 14 PSI in compressed 3 times to 42 total, or 3 times what the atmospheric is, just believe me 3!) so you are taking X amount of air and compressing it into a space aprox 3 times smaller. That’s how you can get a lot more air and still keep the stock turbo on a lot of these setups.
Now the bigger the turbo, the more momentum you have to over come to spin them up. So what a trip setup does is replace the big atmospheric turbo with 2 smaller turbos in parallel that move the same amount of air, they just spool quicker b/c of less mass to overcome. Then the twins in parallel both dump into the intake of the third turbo that’s mounted on the block .
Every sequential or triple turbo setup always has the exhaust power the second stage of compression (the one on the top of the engine) then power the atmospheric turbos.
Exhaust
Once you are done working the air you want to get it out of the way, so a turbo back exhaust will help some. There is very little loss of spool up time by doing this. You want the resistance to be the turbine, not the pipe after the turbine (again the delta or change over there turbine). With flows close to stock the OEM manifolds do just fine, however you want the backpressure to come from the turbine, not the piping going to the turbine so with hot setups aftermarket manifolds and up pipes help.
No, I don’t know what size turbos work well together in twin/triple setups so don’t ask me, there are other people here that have the experience actually making this stuff work. This was long as hell and I wrote it one night after work so I’m sure there’s spelling mistakes in there but there you go. If you see something wrong or not clear let me know and I’ll fix it, hope it helps!
First off, I'm not a turbo expert, I have a lot of knowledge on the concept of turbos (studied jet engine design as my major, same idea as turbos) and I have been playing around with turbo trucks for 8 years now. SOOO I can answer how does this work, NOT which turbo should I get for my setup etc.
There is way too much info here lol.
What is a turbo and how does it work?
Ok so here is the basic idea behind the turbo, the compressor does work on the ambient air forcing more air into a set space (your 6.6L engine). This way when your turbo is spooled up its like having a much bigger engine displacement. Now, you cant have something for free so you need to power this compressor. A supercharger is hooked directly to the engine and uses the engine as power. The downside to this is you are taking a lot of the power the engine is making and running the supercharger and not putting it to the ground. A turbo has a turbine that is in the exhaust flow that powers the compressor. While it does rob the engine of some performance in the form of backpressure in the exhaust, its not nearly the same amount as a supercharger. The downside of a turbo is lag, since a supercharger is hooked to the engine mechanically it revs the same as the engine, where the turbo needs the engine to rev, make more exhaust then spool up.
Thermodynamics 101
Ok there is a few principals you need to know to fully understand what goes on. First off, heat in energy. If you do work on air you are energizing it and total temperature will go up, even in a perfect machine. Same thing when you make air do work for you, the total temp will drop. So even if you made a perfect compressor, the total temp of the air is going to go up depending on how much work you do to it. And on the turbine side, the temp is going to drop depending on how much work you are making the air do. If you put a EGT probe on both sides of the turbine, the would read very close to the same when you were not making boost, but on a stock truck it would be about a 300* drop at full boost.
One more thing, the baseline for the atmosphere is approximately 14PSI at sea level, so when your gauge says 0 PSI its really 14PSI total, it is saying there is 0PSI difference from your setup and the atmospheric pressure.
What is a wastegate and why do VVTs not have one?
A wastegate is just that, a valve that opens up to allow extra exhaust to bypass the turbine therefore providing less power to the compressor to prevent the turbo from over boosting/over speeding. A traditional turbo has vanes that guide the exhaust to the turbine to spin it like a pinwheel. A Variable Vane Turbo has vanes that can move, they close down at lower power settings to build more back pressure (and temperature at lower power settings) spooling the turbo quicker. Then as more exhaust is made they open up, and keep the backpressure at such a point to prevent over boosting. The exhaust flowing over the variable vanes is what makes VVTs whistle like they do.
Why do I have a my boost tubes going to this big radiator on the front of my truck? (its called a CAC)
Like I said before, when you do work on air (pressurize it) you create heat. You want the air entering your engine to be as cold as possible. Power is made from the change of the energy state within the cylinder driving the piston down by burring fuel, which creates a lot of heat. Your engine can only take some much heat before you cause parts to fail. So to make more power, you either make the output hotter, or the input colder so you can have a bigger rate of change (there’s some more thermo 101 for you!) so your CAC reduces the total energy of the air going into the engine, while still keeping the amount of air going in, just cooler. That way you can add more fuel and keep the total temp down.
How do I make my turbo make the most amount of boost possible?
Take one of your boost tubes off and either crush it or fill it full of something. Remember, its not PSI alone that you want, its total airflow, so PSI with the only resistance coming from the engine itself. Turbos are designed to work within a certain range of change is pressure (delta P) and airflow (called a MAP). If you take a turbo outside of its MAP your not really going to get much more airflow, but you will do a lot more work on the air in the form of total temp rise, not good. Now you can push your stock turbo a little more than factory, but not much more you are just overspeeding your turbo and making heat with very little airflow gain.
What is a turbo fart/ strange sound when I go from wide open to idle fast?
At WOT you are making a lot of exhaust and your engine is using a lot of air. When you let off fast you take away that exhaust and the need for the airflow causing a spike in the boost PSI (like shutting a door on the intake). With the drop in exhaust the turbine cannot provide enough power to keep the compressor turning, and the compressor stalls and allows the air to flow backwards out the intake. In extreme cases it can even turn the compressor into a turbine and spin the turbo backwards. Not really good for the turbo. To prevent it just let out of the throttle slowly if you can help it so everything has time to react.
Twins compounds and triples
First off two terms: sequential and parallel. Sequential is one turbo feeding another one, so one will pull air in from the atmosphere and the output feeds the input on the next turbo. Parallel both turbos are pulling air from the atmosphere and dumping it together to the engine, one does not feed the other. Every twin gasser I know if is parallel. Most of the diesel “twins” are really sequential setups. Just as a single turbo crams more air into a set space (6.6L) a sequential setup as a turbo cramming more air into the intake of the second turbo. Think of it as the most awesome air intake ever. Now a turbo MAP only cares about how much the CHANGE in pressure over the compressor is. So if the pressure at the intake of the turbo is 100 PSI and the output is 130 PSI, it is exactly the same to the turbo as if it was 0 PSI at the intake and the output was 30PSI. (but the boot holding the output tube on would care!!!) That is why you can get so much boost out of a sequential setup.
The benefit of a sequential setup over a big single is you still have the primary turbo that is small, and will spool quicker and much smother. The downside is all the extra piping that goes with it.
Now for the new cool thing, triples.
In a sequential set up, the atmospheric turbo (the first one the air sees) has to be big, if you are running 28PSI off this first turbo then your compression ratio is 3 (atmospheric 14 PSI in compressed 3 times to 42 total, or 3 times what the atmospheric is, just believe me 3!) so you are taking X amount of air and compressing it into a space aprox 3 times smaller. That’s how you can get a lot more air and still keep the stock turbo on a lot of these setups.
Now the bigger the turbo, the more momentum you have to over come to spin them up. So what a trip setup does is replace the big atmospheric turbo with 2 smaller turbos in parallel that move the same amount of air, they just spool quicker b/c of less mass to overcome. Then the twins in parallel both dump into the intake of the third turbo that’s mounted on the block .
Every sequential or triple turbo setup always has the exhaust power the second stage of compression (the one on the top of the engine) then power the atmospheric turbos.
Exhaust
Once you are done working the air you want to get it out of the way, so a turbo back exhaust will help some. There is very little loss of spool up time by doing this. You want the resistance to be the turbine, not the pipe after the turbine (again the delta or change over there turbine). With flows close to stock the OEM manifolds do just fine, however you want the backpressure to come from the turbine, not the piping going to the turbine so with hot setups aftermarket manifolds and up pipes help.
No, I don’t know what size turbos work well together in twin/triple setups so don’t ask me, there are other people here that have the experience actually making this stuff work. This was long as hell and I wrote it one night after work so I’m sure there’s spelling mistakes in there but there you go. If you see something wrong or not clear let me know and I’ll fix it, hope it helps!
