9 Second (STS) REAR mount setup
@15# at 6500RPMs a 408 will consume 86lbs of air and a 370 will consume 78lbs. So in order to maximize efficiency you would need to run a bigger turbo on the 408 in order to be in the same efficiency range as you would on the 370 since its consuming more air.
on a T76 a 370 would be right on the edge of 65% efficiency range at 15# and the 408 would be out of the efficiency range. Granted its not the biggest difference but you get the idea.
on a T76 a 370 would be right on the edge of 65% efficiency range at 15# and the 408 would be out of the efficiency range. Granted its not the biggest difference but you get the idea.
Last edited by ABeasst; Jan 31, 2006 at 11:45 AM.
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From: Spring Hill, TN
Originally Posted by ABeasst
@15# at 6500RPMs a 408 will consume 86lbs of air and a 370 will consume 78lbs. So in order to maximize efficiency you would need to run a bigger turbo on the 408 in order to be in the same efficiency range as you would on the 370 since its consuming more air.
on a T76 a 370 would be right on the edge of 65% efficiency range at 15# and the 408 would be out of the efficiency range. Granted its not the biggest difference but you get the idea.
on a T76 a 370 would be right on the edge of 65% efficiency range at 15# and the 408 would be out of the efficiency range. Granted its not the biggest difference but you get the idea.
I think you might have forgotten that the smaller displacement motor will run to higher revs. longrange4u provided a scenario whereby the 370 would spin to 6400 while the 408 would spin to 5900. If the real values are different this would all have to be rehashed.
Given those parameters, and assuming 100% VE the smaller motor would consume a max of 685 cfm while the big one would consume 696 cfm. This would be if normally aspirated.
That's a difference of 1.6 or 1.7%
I'm not really saying that I wouldn't choose a smaller turbo for the smaller engine...I probably would to keep the boost threshold down and to put the maximum efficiency in an rpm range that I like on the street.
But compressor maps are based on the engine's air consumption, not its displacement.
I've already pissed off one guy today, I will probably stop pressing this point. Besides, I could be wrong.
i dont see why he would rev the 408 so low.....he should be revving to 6500 on that setup...and the 370 could be revved 7k if he wanted...but he'd probably stay at 6500 to be on the safe side anyways.So then you have to compare what lb/min of flow each of those would be at at 6500rpms....where the 408 will obviously outflow the 370.But hes going to need a much larger turbo for the 408 so it wont choke out when revved that high.All things equal the 408 would make more power....BUT if the 370 was setup right it would take him to his power goal and spool faster than the 408 would.Thereby saving him quite a bit of money on the motor and turbo size.When comparing motors and turbos you have to stick to the same ammount of boost and rpms to make it fair.There was a thread not too long ago about front vs rear mounts and how a comparision was done but "wasnt fair" because the rear mount turbo wasnt choose specifically for its application.So lets say it was,but to make it fair the front mount has to have its choice as well,the front still wins.You have to compare apples to apples.just thinking outloud
The challenge that I have in what I have learned is that... The 408 will far outflow the 370 at similar RPM's. What is not addressed here but we talked about in another thread is that you must have a reduced A/R for a rear mount setup vs a front mount. This affects the turbo size and air flow your capable of (further choking off the 408). At peak RPM the 370 may fall off efficiency in the turbo map... but it will stay in optimum efficiency longer with a reduced A/R rear mount turbo..
Again this is just what I am learning... if I am off someone correct me.
Again this is just what I am learning... if I am off someone correct me.
Well, if you stay stock cubes, I'd say 700rwhp to hit 9's with a T56. I think you can get there with 650rwhp but I don't know how much harder it is to get there with the manual.
I went 10.3 with like 600rwhp.
I went 10.3 with like 600rwhp.
but your Th400 swallowed up alot of HP, and nothing puts the power down to the ground like a 400 or glide.
i think youll need a little more then 700rwhp to do it with the M6, unless your suspension is set up perfect.
im guessing about 800ish, i though MM and roman took 900rwhp to get there and those were high nines.
i think youll need a little more then 700rwhp to do it with the M6, unless your suspension is set up perfect.
im guessing about 800ish, i though MM and roman took 900rwhp to get there and those were high nines.
Originally Posted by longrange4u
The challenge that I have in what I have learned is that... The 408 will far outflow the 370 at similar RPM's. What is not addressed here but we talked about in another thread is that you must have a reduced A/R for a rear mount setup vs a front mount. This affects the turbo size and air flow your capable of (further choking off the 408). At peak RPM the 370 may fall off efficiency in the turbo map... but it will stay in optimum efficiency longer with a reduced A/R rear mount turbo..
Again this is just what I am learning... if I am off someone correct me.
Again this is just what I am learning... if I am off someone correct me.
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I think you guys are missing something rather important, if you want the thing to spool quickly and are limited by turbo size remember this, people we know and do business with are making over 400 to the wheels with lancer EVO's on STOCK turbochargers, that being said, YES they are out of the effective efficient range of the turbo, BUT it still works and delivers extreme acceleration in the lower RPM's and still delivers what they want up top. The thing to take from this is that just because the map says it it getting close or slightly over the edge, does not mean it can't do the job. I personally think the added bottom end would offset any small loss of HP up top, especially in a stick car. Our project if you saw it is exactly what you are trying to do but with an auto, I am confident this will work out and I am sure you can do it as well, the only real reason it has not been done yet is nobody has REALLY tried to set the car up completely for the turbo application.
-Bryan
-Bryan
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From: Spring Hill, TN
Originally Posted by Race-Prep
I think you guys are missing something rather important, if you want the thing to spool quickly and are limited by turbo size remember this, people we know and do business with are making over 400 to the wheels with lancer EVO's on STOCK turbochargers, that being said, YES they are out of the effective efficient range of the turbo, BUT it still works and delivers extreme acceleration in the lower RPM's and still delivers what they want up top. The thing to take from this is that just because the map says it it getting close or slightly over the edge, does not mean it can't do the job. I personally think the added bottom end would offset any small loss of HP up top, especially in a stick car. Our project if you saw it is exactly what you are trying to do but with an auto, I am confident this will work out and I am sure you can do it as well, the only real reason it has not been done yet is nobody has REALLY tried to set the car up completely for the turbo application.
-Bryan
-Bryan
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I am not sure I understand your comment but I am saying the turbo will perform better than the map says it will, it just becomes diminishing returns, and this is from my and others experience. How else do you explain a turbo designed for 200ish WHP making 400+?
-Bryan
-Bryan
It's really a balancing act,
between what you can afford,
what you can physically fit,
and your engine choices.
If I had a 408ci, I would expect
that a 76mm would be small,
88 would be okay, but a 91 would
be okay too... But look at how
big some of the biggest turbos
are.
between what you can afford,
what you can physically fit,
and your engine choices.
If I had a 408ci, I would expect
that a 76mm would be small,
88 would be okay, but a 91 would
be okay too... But look at how
big some of the biggest turbos
are.
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There's no doubt there is more he can likely do with it, but I feel a gts76 with the right A/R would do what he desires as long as the traction was there especially since he wants what I am doing soon!
-Bryan
-Bryan
Originally Posted by Race-Prep
I am not sure I understand your comment but I am saying the turbo will perform better than the map says it will, it just becomes diminishing returns, and this is from my and others experience. How else do you explain a turbo designed for 200ish WHP making 400+?
-Bryan
-Bryan
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From: Spring Hill, TN
Originally Posted by Race-Prep
I am not sure I understand your comment but I am saying the turbo will perform better than the map says it will, it just becomes diminishing returns, and this is from my and others experience. How else do you explain a turbo designed for 200ish WHP making 400+?
-Bryan
-Bryan
Is there a rule of thumb for what RPM we might want maximum efficiency with a turbo? If a given turbo reaches it's 80% efficiency between a certain RPM range on a given engine then what range are we looking for?
in smallness for a turbo i would be less concerned about the comprssor being out of range, but would keep an eye on the back pressure.
i wonder why alot of people are popping head gaskets when they dont have a bad tune, i think the two are related.
i wonder why alot of people are popping head gaskets when they dont have a bad tune, i think the two are related.
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Bryan, APS BB convertion on the turbo and other bolt on stuff will net you 485bhp at the crank now!
i agree with you, everyone wants to run a bigger turbo. why? oem stuff is normaly very small so they spool up low down the rev range and give really good low down torque and boost. and as (i think you said it) its area under the graph that makes a car quick and what racers aim for, not peak figures.
and so what if you run a little out the effective range? it just means you will enter it earlier and it will spool up faster. what are the effects of running outside the effetive range? slightly hotter temps?????
thanks Chris.
i agree with you, everyone wants to run a bigger turbo. why? oem stuff is normaly very small so they spool up low down the rev range and give really good low down torque and boost. and as (i think you said it) its area under the graph that makes a car quick and what racers aim for, not peak figures.
and so what if you run a little out the effective range? it just means you will enter it earlier and it will spool up faster. what are the effects of running outside the effetive range? slightly hotter temps?????
thanks Chris.
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Wish there was some uniform "area under the curve" HP/TQ measurement that might more accurately describe torque applied throughout the rpm range instead of just a peak measurement. It would help to quantify that "low-spooling" behavior and demonstrate the effects up top as well... and should more accurately predict acceleration benefits.
Originally Posted by smokinHawk
in smallness for a turbo i would be less concerned about the comprssor being out of range, but would keep an eye on the back pressure.
i wonder why alot of people are popping head gaskets when they dont have a bad tune, i think the two are related.
i wonder why alot of people are popping head gaskets when they dont have a bad tune, i think the two are related.
Hawk... well said. My largest concern with a 408 and a GT-42 76 rearmount combo. I believe that the turbo would spool fast and perform well, however remember that we have to keep in mind back pressure of exhaust. Jose told me that anything over 2.0 starts to get troublesome... Looking at more then simple efficiency, a 1.01 AR on the above turbo would not be able to choke down the exhaust fast enough (Efficiently or not) to keep the engine from producing considerable exhaust back-pressure. You will see this at even lower RPM's with the 408 (57-5900RPMS).... That is why I consider the 370... yes it does have the capability to take the turbo out of its efficiency range, but is much less likely to overflow the turbo's consumption capabilities... (Wow... I feel like I am actually learning some of this) 
Is the criteria a quick spooling street car or a 9 second car? I'm not suggesting you can't have both, but I hear a lot of talk about area under the curve in this thread... last time I checked very few 9 second cars spend little (if any) time under 5000 rpm.
Smaller turbos 'feel' very peppy on the street, but big turbos generally rule the track.
Smaller turbos 'feel' very peppy on the street, but big turbos generally rule the track.
Originally Posted by longrange4u
Hawk... well said. My largest concern with a 408 and a GT-42 76 rearmount combo. I believe that the turbo would spool fast and perform well, however remember that we have to keep in mind back pressure of exhaust. Jose told me that anything over 2.0 starts to get troublesome... Looking at more then simple efficiency, a 1.01 AR on the above turbo would not be able to choke down the exhaust fast enough (Efficiently or not) to keep the engine from producing considerable exhaust back-pressure. You will see this at even lower RPM's with the 408 (57-5900RPMS).... That is why I consider the 370... yes it does have the capability to take the turbo out of its efficiency range, but is much less likely to overflow the turbo's consumption capabilities... (Wow... I feel like I am actually learning some of this)Something you said actually made me think of something,in the other thread about rearmounts vs front mounts it was said and pretty much proved that a rearmount is less efficient as getting the air and heat to the turbo correct?If thats true then wouldnt you be able to use a larger motor with a smaller turbo to get in the efficiency range of a front mount setup with a motor suited to the turbo?I dont know if i explained that right or it made sense but it makes sense in my mind.Wouldnt that work?