Help turbo peeps look here please
Thread Starter
Joined: Sep 2004
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From: Fairview NC (near Charlotte)
Help turbo peeps look here please at what RPM should I be making peak power with a stock 2002 LS1 engine with LS6 valve springs on a Precision T67 Q trim non BB turbo
it seems to me to peak kind of early at around 5000 and then it falls off really fast
I am making around 7 Pounds of boost
my kit is the PTS with the Front mount air to air intercooler
the engine is compleatly stock other than the valve springs
I am making 475 RWHP through a 9 inch rear with 3.50 gears but it is at 5000 RPM by 5500 it had fell off 30 or so HP
it seems to me to peak kind of early at around 5000 and then it falls off really fast
I am making around 7 Pounds of boost
my kit is the PTS with the Front mount air to air intercooler
the engine is compleatly stock other than the valve springs
I am making 475 RWHP through a 9 inch rear with 3.50 gears but it is at 5000 RPM by 5500 it had fell off 30 or so HP
The LS6 valvesprings are your 1st problem.. 
At least get some Comp 918's (I use those with your boost) or get some good duals.
The LS6 lose a lot of their strength when the metal get hot. I saw a test between stock springs and 918's on an STS Formula. It was suprising. I think it gained 13 horsepower just from the valvespring change!
At least get some Comp 918's (I use those with your boost) or get some good duals.
The LS6 lose a lot of their strength when the metal get hot. I saw a test between stock springs and 918's on an STS Formula. It was suprising. I think it gained 13 horsepower just from the valvespring change!
Thread Starter
Joined: Sep 2004
Posts: 717
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From: Fairview NC (near Charlotte)
at 5100 it was around 467 uncorrected and by 5600 it was 406
was on the stock LS1 valve springs
I cant find the run that I made on the LS6 springs but it was pretty colse to the same
it is holding boost pretty good for the entire range
if it is valve float would I not be able to feel it or at least hear it
was on the stock LS1 valve springs
I cant find the run that I made on the LS6 springs but it was pretty colse to the same
it is holding boost pretty good for the entire range
if it is valve float would I not be able to feel it or at least hear it
^^ It would still hold boost... but your valves still aren't being controlled properly with those springs.
You need an upgrade asap. Power isn't supposed to fall like that. The engine pulls the entire range of whatever cam but much harder when boost is envolved. You should be going way past 5.5k rpm before nosing over that hard.
You need an upgrade asap. Power isn't supposed to fall like that. The engine pulls the entire range of whatever cam but much harder when boost is envolved. You should be going way past 5.5k rpm before nosing over that hard.
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I don't think its valve float as the boost levels are not quite that high and the RPM is so low.
I do think it has something to do with the turbo sizing and back pressure.
VE for a forced induction car can be derived to a function of exhaust pressure/intake pressure raised to some exponent involving the ratio of specific heats. What I'm saying w/ this is as the ratio (intake pressure/exhaust pressure) goes down VE falls.. which means MEP falls and the car makes less torque/hp.
A way to fix this would be to get a bigger turbo so exhaust pressure doesn't climb as fast with airflow (make the top term in the ratio smaller)
OR
make the top term in the ratio higher.
This is easy to prove to yourself. If a stock engine is suddenly boosted by 8psi across the board the power gains would be offset at higher RPM (or airflow) by the power requirement (exhaust gas) to drive the forced induction at those higher airflows.
No free lunch. If a supercharger takes 35hp to turn 8psi at 300g/sec it might take 50hp to turn 8psi at 500g/sec
I do think it has something to do with the turbo sizing and back pressure.
VE for a forced induction car can be derived to a function of exhaust pressure/intake pressure raised to some exponent involving the ratio of specific heats. What I'm saying w/ this is as the ratio (intake pressure/exhaust pressure) goes down VE falls.. which means MEP falls and the car makes less torque/hp.
A way to fix this would be to get a bigger turbo so exhaust pressure doesn't climb as fast with airflow (make the top term in the ratio smaller)
OR
make the top term in the ratio higher.
This is easy to prove to yourself. If a stock engine is suddenly boosted by 8psi across the board the power gains would be offset at higher RPM (or airflow) by the power requirement (exhaust gas) to drive the forced induction at those higher airflows.
No free lunch. If a supercharger takes 35hp to turn 8psi at 300g/sec it might take 50hp to turn 8psi at 500g/sec
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TECH Resident
Joined: Jan 2004
Posts: 832
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From: Castro Valley, CA
Hey, Darren... the fun just doesn't end, does it?
What's the A/R on that T67? And have you ever given it a run with open exhaust?
I've got some weird top-end stuff going on with mine, too... the dyno trace wobbles up and down by about 40 rwhp/rwtq once the motor's past 3500 rpm. Valvesprings are going to be checked today.
Anyone else running a front-mount T67?
What's the A/R on that T67? And have you ever given it a run with open exhaust?
I've got some weird top-end stuff going on with mine, too... the dyno trace wobbles up and down by about 40 rwhp/rwtq once the motor's past 3500 rpm. Valvesprings are going to be checked today.
Anyone else running a front-mount T67?
It may just be the curve a T-67 provides on a big V8... It's a .96 A/R, right? I don't think the exhaust would be the part getting choked. T-67's have been great at rear-mounts, but maybe this is their limitation, being on the front... Unless it is in fact a valvetrain/tuning/fuel problem.
Any dyno's of FMounted T-67's out there? Maybe someone should view a compressor map/consumption chart. I did with a T-76, and the efficiency was actually surprising... Smaller turbos really do have their work cut out for them, even on 346 cubes.
Any dyno's of FMounted T-67's out there? Maybe someone should view a compressor map/consumption chart. I did with a T-76, and the efficiency was actually surprising... Smaller turbos really do have their work cut out for them, even on 346 cubes.
Thread Starter
Joined: Sep 2004
Posts: 717
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From: Fairview NC (near Charlotte)
Originally Posted by Asmodeus
what pump and injectors are you using? what is the injector duty cycle %? how's your A/F ratio?
walbro 340 intank 225 pump
60 pound injectors
not over 60 %
Fuel sounds just fine...
Maybe the valve float is minor to negligible, with the turbo adding a bit to the limitations?
Paging Dr. Turbo? Front-mount T67... Is this normal? At what rpm does this turbo choke?
Maybe the valve float is minor to negligible, with the turbo adding a bit to the limitations?
Paging Dr. Turbo? Front-mount T67... Is this normal? At what rpm does this turbo choke?
