After reading Trents thread I just can't wrap my brain around this. Unless I'm miss reading something how does a setup like this equal to lower DP and boost but more power? Or is all of that just speculation at this point?
Advantages of a parallel setup?
- Thread starter Dozerboy
- Start date
If this helps at all..
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 ram 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. So let’s say you do a S475 over stock, your truck will spool the same on the bottom end as stock, only once the stocker is spooled up the S475 will be lighting and it will keep boosting
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 ram 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. So let’s say you do a S475 over stock, your truck will spool the same on the bottom end as stock, only once the stocker is spooled up the S475 will be lighting and it will keep boosting
well I like to learn, so instead of saying not true, just correct me. Were adults here........sometimes
Typical turbos compressor wheels are only designed to run up to pressure ratio of 4 to 1. Pressure ratio is calculated
Pr = (pressure ambient+boost pressure)/pressure ambient
Here is some basic turbo techno stuff. Most diesel run more boost than gasers do. Any more pressure turbos like to break shafts. also they become less efficent, basically are operating in choke, just making hot air and will require more energy to create boost.
http://turbobygarrett.com/turbobygarrett/turbo_tech_advanced
http://turboneticsinc.com/content/compressor-maps
Operating two turbo in sequential configuration, you can get higher boost levels, at a lower intake inlet temperature (typically if you selected the correct turbos)
Pr = (pressure ambient+boost pressure)/pressure ambient
Here is some basic turbo techno stuff. Most diesel run more boost than gasers do. Any more pressure turbos like to break shafts. also they become less efficent, basically are operating in choke, just making hot air and will require more energy to create boost.
http://turbobygarrett.com/turbobygarrett/turbo_tech_advanced
http://turboneticsinc.com/content/compressor-maps
Operating two turbo in sequential configuration, you can get higher boost levels, at a lower intake inlet temperature (typically if you selected the correct turbos)
Turbos work on pressure ratio. If an atmosphere turbo is being fed atmospheric pressure of 14.5 psi (this assumes there is no restriction in the intake and sea level) and is showing 30 psi on a guage, it is working at approximately a 3:1 pressure ratio, (30+14.5)/14.5=3.07. If you are feeding another turbo with that turbo, you will have 44.5 psi on the inlet of the turbo. In order for it to be the same pressure ratio, it would need to be putting out 133.5 psi or 119 on a gauge.
Here are my thoughts on parallel turbos, right or wrong. When you compound turbos, you lose some efficiency. Running them in parallel allows you to get the same amount of air and efficiency of a large single but with quicker spool up. The only problem is that since diesels run at such a low RPM, it is harder for them to take in air (remember an engine is an air pump). Running compounds allows you to build more boost pressure which forces more air into the engine in a shorter amount of time. I think heads and cams will be more important with parallel twins that they are with compound twins.
Would you expand uppon that statement some josh? I was under the impression that they were very efficient when sized properly, hence the very manageable EGTs and whatnot. I suppose that each turbo as a unit itself could be less efficient in a compound setup, but the two combined are gennerally more efficient than each on its own when run inside the design parameters of the set. Or am i blatantly missing something obvious? LOL!
I could be wrong in this, but here's the way I look at it. Say your turbos have 85% efficiency. Your first stage is giving 85% of what is possible, then when it goes to the second stage gives you 85% of the original 85% making it only 72% of the original potential. I think the reason it isn't much of a problem is because the primary turbo is so large and the boost pressures are so high, you get a bunch of air. Look at what kind of power range you run with a single compared to a compound setup with a comparable size primary. You don't run into problems with compound efficiency until you really push them. A good example is a stock turbo twin setup using an S475 or GT4202 as the primary in a compound setup compared to how they do in a single setup. They are getting pushed really hard when you get up above 700 HP in a compound setup, but as a single, they are good up to about 800 if you have the fuel to drive it. It is easier to make power with compounds with cooler EGTs, but you have to oversize them.Would you expand uppon that statement some josh? I was under the impression that they were very efficient when sized properly, hence the very manageable EGTs and whatnot. I suppose that each turbo as a unit itself could be less efficient in a compound setup, but the two combined are gennerally more efficient than each on its own when run inside the design parameters of the set. Or am i blatantly missing something obvious? LOL!
I think heads and cams will be more important with parallel twins that they are with compound twins.[/QUOTE]
I believe that statement is 100% spot on! I was thinking this also, when running parelle turbos i think you will see more head porting, cams, y bridge mods, intakes etc... like you said
I believe that statement is 100% spot on! I was thinking this also, when running parelle turbos i think you will see more head porting, cams, y bridge mods, intakes etc... like you said
Think about whats the advantage of running twin parrallel turbos over a single? Almost none, besides the fact you can say you have twins under the hood. There are some slightly spool-up improvements running twins in parallel, but all the extra air tubing under the hood would be a night mare.
Most twin turbo sequential turbo trucks, don't run 130psi, unless they have the wrong turbos. I shoot for 70-80psi of boost. The biggest beneift to twins, is you can cram more mass flow into a smaller turbo, and still have decent spool-ups. My best twins set-up to date is a GT3582R over a S478LI. Wicked fast spool-up, almost gaser like. Pulls hard to 80psi. Drive pressure is balanced with boost. Egts for stockish trucks are typically under 1300 deg's. :woott:
Most twin turbo sequential turbo trucks, don't run 130psi, unless they have the wrong turbos. I shoot for 70-80psi of boost. The biggest beneift to twins, is you can cram more mass flow into a smaller turbo, and still have decent spool-ups. My best twins set-up to date is a GT3582R over a S478LI. Wicked fast spool-up, almost gaser like. Pulls hard to 80psi. Drive pressure is balanced with boost. Egts for stockish trucks are typically under 1300 deg's. :woott:
For the most part, I agree with you on the parallel turbo stuff.
Also, nowhere did I ever say (assuming you were making reference to my pressure ratio post) anyone was running 130 PSI of boost pressure. Your experience with a Cummins doesn't translate over directly to a Duramax. No way would that turbo setup run 80 lbs of boost on a Duramax. Especially not without some major fuel system upgrades. I was running an S366 with a GT4718 and only seeing about 65 PSI on my boost gauge. That was with dual CP3s and 80% over injectors pushing enough fuel to run 11.13 @ 123 in a 6800 lb truck.
i just cant figure out how a single bank is gonna spool a turbo with the low rpms these trucks run. im real curious to see the results...
I think it will just take time to see what supporting mods is needed to make them work optimally porting, cam, ETC. If you can spool a big single you should be able to spool 2 smaller turbos with the same output without much more effort.
Thanks Josh that makes sense to me
Thanks Josh that makes sense to me
The reason for parallel turbos is simple.
Most use it cause it reduces the lag compared to a single, hold your powerband better, and is more efficient. Reasons for running a single is its cheaper and generally more top end power. Try not to over think it.
Most use it cause it reduces the lag compared to a single, hold your powerband better, and is more efficient. Reasons for running a single is its cheaper and generally more top end power. Try not to over think it.
I also could be wrong, but I suppose it depends on your definition of power and efficiency. A big single may create higher peak hp, but would twins have more area under the curve? ( due to better numbers in the low to mid range )
I would think that if you measured egt after your last ( or only ) turbo, that twins would have a cooler temp. ( less heat lost to atmosphere, better overall efficiency).
It will certainly be interesting to see what they are capable of.
I agree that parallels compared to a big single have few advantages. Look at the tuner cars that come stock with parallel turbos and guys end up swapping to a huge single when they get serious about racing. The reason you see cars like Steve Morris' 3000+hp 572 Cube Ford running parallel is that it is running parallel Billet BullsEye S588s - there isn't a single that can flow the same air as those two chargers combined and it has 572 cubes turning 7000+ RPM. On my race truck I am torn between running an S500 or GT47 as a single or going with 2 S300s parallel.
Like Josh explained a turbo doesn't run at 100% effeciency, in compounds the big turbo has it's loss then the small turbo has it's loss. Which, just as he explained, is why an S480 as an atmosphere in compounds is worth less power than as a single - in the top end the small charger is just getting in the way. The engine is an air pump and cares more about lbs/hr of air that is shoved in than it does about boost pressure. Lets say a charger pushes 100 lbs/min as a single, then with a small charger in the way with it's 15% effeciency loss puts you down at 85 lbs/min - the result is higher boost but less flow and less power. The limitations on running a big single are being able to spool it for your use, but turbos have come a long way recently, both in spool up and flow. The right S300s are doing over 800 rwhp and the right S400s are spooling much easier than they used to - meaning most people can run a single that meets their power and spool up needs all in one.
As was mentioned your best twin setups have been on dodge where a 62mm turbo is a decent sized upgrade. What kind of power was that 62/78 setup worth? Duramax's have dynoed 600+ rwhp on a stock turbo on fuel. This past weekend I had a customer run 12.34 @ 111 on a horrible 60' beside another customer that ran a 12.33 @ 104 because he went into a fuel limp before the end and was slowing down through the traps - both on stock turbos on fuel only in full weight trucks on street tires. There is no way I would recommend a 62mm turbo to a Duramax customer. The smallest I would recommend is an S366 - they spool awesome for daily driving and towing, even better in billet and BatMo form. They have dynoed 850+ rwhp by themselves, which I'm pretty sure is as much or than the 62/78 setup you are talking about would do - all at a lower cost and with less clutter under the hood. The LMM we just put a Double Bat 366 on holds 5 PSI any time you are accelerating the slightest bit (like taking a half mile to get from 45 to 55), gradually add throttle and the gauge follows your foot; roll in hard and it will shoot to 50 PSI and snatch the tires loose.
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I just picked 100/130PSI as a random number to explain the concept I should have used more realistic numbers for the Dmax-I left out the loss in the turbos b/c I was trying to keep it simple and explain multiple stages of compression, sorry if I confused people on this