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.
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.