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Finally we have found out what keeps us from boosting 30 psi and what causes high ehaust gas temperatures: EXHAUST GAS BACK PRESSURE.

Engine is inline Euro M3 3,2L. JE Forged pistons with 6,8 cr. Turbocharged and front mount intercooler air to air. Fuel octane was 105.

Turbocharger: Garrett. Exhaust turbine GT40. A/R 1,06. Wheel trim 84. Wheel diameter 2,16/2,36.

We had very safe AFRs such as 11,5:1. But EGT was 1450 F at 140 mph. The pull was made from 62 mph till 140 mph. At 140 mph EGT was 1450 F. We backed off and did not want to see higher than 1450 F. Timing could be advanced and we advanced timing. Starting from 4000 rpm till redline at 8200 rpm, timing was increased gradually and from 5000 rpm till 8200 rpm 10 degrees of advance was dialed in. We were able to decrease EGT 50-70 F but were afraid to add more timing advance at these high boost levels.

WE measured the exhaust back pressure before the exhaust turbine of the turbocharger. At 26 psi of manifold boost we have seen 63 psi of exhaust back pressure.

The ratio of exhaust gas back pressure to intake pressure should be maximum 2:1. Is this correct?

Now my question is: Can I shave off the exhaust turbine of the turbocharger in order to reduce exhaust gas back pressure?
Shaving may be done in three ways:
1- Shave off the exhaust turbine housing's entrance, this is the area where the exhaust gases come into the turbine.
2- Shave off the turbine housing's snail shaped curves.
3- Shave off the area where the turbine housing is bolted into the dump pipe.

Which method would reduce back pressure?

There is one more option which is expensive: as I have a Garrett, the exhaust turbine can be changed by a GT40 housing with 2,45/2,68 wheel diameter or with a GT42 turbine housing which has 1,22 A/R, 78 wheel trim and 3,03/3,43 wheel diameter.


What should I do? I would like to solve this back pressure issue by just shaving off the exhaust turbine.
 

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What size exhaust and DP is on the car?

Adam
 

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2slow2jz said:
run a less restrictive exhaust system post turbo
agreed, if youre talking 1000hp, youre going to want at least a 3.25-3.5inch downpipe bolted up to a very straight exhaust with a big ID. personally at that power level, id think about getting a custom 3.75 or 4 inch downpipe mated to a 4 inch exhaust.

i had no idea the GT40 was capable of 1000hp. i thought the GT42 was only capable of about 1,050 crank.
 

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Discussion Starter #6
Adrocktt: the dump pipe ID is 3,2". After the dump pipe there are two separate pipes with 2,4" ID each. No cats, no resonators, and a fully free muffler.

LYTLDiablo: with the GT 40 we did not get 1,000 hp. We just trying. Could you please tell me where to see the 1,050 crank hp of the GT 42?
 
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souns like there is something possibly wrong ith the turbo then. maybe the center section is coked up and causing the shaft to bind up. or maybe a bad backfire jacked up the turbine wheel
 

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mert said:
Adrocktt: the dump pipe ID is 3,2". After the dump pipe there are two separate pipes with 2,4" ID each. No cats, no resonators, and a fully free muffler.

LYTLDiablo: with the GT 40 we did not get 1,000 hp. We just trying. Could you please tell me where to see the 1,050 crank hp of the GT 42?
Open wastegate or closed? I am still having trouble imagining your setup. Sounds like the DP/exhaust combo would be the 1st place to start out versus modifiying turbo characteristics. Immediate post turbo our GT40/42 cars run ~4" ID DP's straight through to a 4" exhaust. Drag cars run 4-5" dp's right out the fender. If you are shooting for 1k hp, make sure post turbo there is not a large restiction, back preassure is not perfered for turbo setups like it is with NA setups.

Adam
 

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mert said:
Adrocktt: the dump pipe ID is 3,2". After the dump pipe there are two separate pipes with 2,4" ID each. No cats, no resonators, and a fully free muffler.

LYTLDiablo: with the GT 40 we did not get 1,000 hp. We just trying. Could you please tell me where to see the 1,050 crank hp of the GT 42?
well let me first say its a rough guess...but heres how i look at it.

supposedly the GT42 53 trim (the bigger one with the 74/102 compressor) can flow 95lb/min of air (on paper)

95lb/min * 10.86 * .85 (15 percent power loss in a manual transmission) = 876.945rwhp or 1,031.7 crank horsepower.

the airflow number im using is just theoretical, and its just an equation to help gauge what a turbo can push, so its far from concrete.

as for your exhaust setup...3.2 ID downpipe is definitely on the small end for a 1,000hp application. also you must remember two 2.4 inch pipes, does not equal a 4.8 inch pipe.

two 2.4 inch pipes = 1.2^2 * 3.14 * 2 = 9.0432 in^2

a mere 3.5 inch (88mm) single pipe would yield 9.61625 in^2

a single 4 inch pipe would have 12.56 square inches of internal area, that is a 39% increase!

and thats not even counting the slight backpressure youre getting from splitting your exhaust up in the first place. youre not running a twin turbo setup, i really dont see any reason you'd want twin exhaust pipes.

actually, id bet that two 2.4 inch pipes have even worse clearance issues than a single 4 inch pipe properly fitted.
 
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Are you sure the 3.5 inch pipe area u came up with is correct? :p
LYTLdiablo said:
two 2.4 inch pipes = 1.2^2 * 3.14 * 2 = 9.0432 in^2

a mere 3.5 inch (88mm) single pipe would yield 9.61625 in^2

a single 4 inch pipe would have 12.56 square inches of internal area, that is a 39% increase!

and thats not even counting the slight backpressure youre getting from splitting your exhaust up in the first place. youre not running a twin turbo setup, i really dont see any reason you'd want twin exhaust pipes.

actually, id bet that two 2.4 inch pipes have even worse clearance issues than a single 4 inch pipe properly fitted.
 

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Dawg said:
Are you sure the 3.5 inch pipe area u came up with is correct? :p
lol yeah.

area = (pi) * r^2
3.5 inch ID = 1.75^2*3.14 (pi) = 9.61625 in^2
 

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LYTLdiablo said:
lol yeah.

area = (pi) * r^2
3.5 inch ID = 1.75^2*3.14 (pi) = 9.61625 in^2
But LYTLdiablo....What's the exact value for pi?

:p

Adrock
 

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oh shut up adam :)

3.141727 or some crap like that on and on and on


/Mark
 
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