Boost loss with stock exhaust - Boost Forum

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Boost loss with stock exhaust
Wednesday, March 22, 2006 7:34 AM
I finally ran the car this morning!! It's a 02 Eco with Hahn stage 2. However, when I went to tune it at boost, I am only seeing about 5 psi. I have not had my exhaust done yet. Does a loss of 3-4 psi of boost seem right for the stock exhaust on there? I was supposed to hit between 85-90psi fuel pressure, but only saw about 80 psi at this boost level. I wan't thinking that the stock exhuast would be that drastic, but any experiences here would be great. Thanks guys.


"If you aren't shifting, then you certainly aren't driving!"

Re: Boost loss with stock exhaust
Wednesday, March 22, 2006 8:25 AM
no, stock exhaust you should not see any "boost loss"



LE61T PTE6262 Powered

Re: Boost loss with stock exhaust
Wednesday, March 22, 2006 8:47 AM
the wastegate from Hahn is a 6-8PSI wastegate. Basically you'll see anywhere from 6-8PSI boost with it. Depending on weather I have seen both in the same day. Your stock exhaust isn't stealing the boost but it is definately killing your power.

The 80PSI fuel pressure is about right for 5PSI though so don't worry about that.



I used to race cars, now I race myself.
5K PB: 24:50
10K PB: 54:26
Re: Boost loss with stock exhaust
Wednesday, March 22, 2006 10:39 AM
Well I ended up adjusting the needle valve on the FMU all the way rich to try to get above 80 psi. It totally stopped at 80 psi. So where should I set the needle valve to if 80 psi is going to be it? I was just going by the Hahn manual which states that under full boost you should see 85-90 psi. I am just being cautious so I don't break anything!!


"If you aren't shifting, then you certainly aren't driving!"
Re: Boost loss with stock exhaust
Wednesday, March 22, 2006 10:41 AM
Sorry, forgot this. So you guys are saying that seeing 5 psi is right? I expected the boost gauge to read at least 8 psi. I guess I don't see how the weather influences the boost level, power I understand but I don't get the boost part. And the weather here is COLLLLD!!!


"If you aren't shifting, then you certainly aren't driving!"
Re: Boost loss with stock exhaust
Wednesday, March 22, 2006 10:51 AM
yea but where are you in relation to elevation?



2000 Camaro V6.
| SLP Loudmouth | CAI Intake | HID's |


Re: Boost loss with stock exhaust
Wednesday, March 22, 2006 11:26 AM
I'm in Indiana, we are pretty flat here. I don't think we are really high above sea level.


"If you aren't shifting, then you certainly aren't driving!"
Re: Boost loss with stock exhaust
Wednesday, March 22, 2006 11:46 AM
I see 6PSI right now. In the summer I normally see 8PSI when running "on the 'gate". THe FMU calibration you have is a 8:1 setup. So for 5PSI boost you are getting a 40PSI fuel jump. For 8PSI boost you would get a ~60PSI jump which is where they get the 85-90PSI number. Don't be so concerned about the pressure. What you need to watch is the AFR. I can maintain a perfect 12.5:1 AFR on 50PSI at WOT as well as at 65PSI. Then again I have bigger injectors and a different calibration for the FMU than you so my pressures are a lot lower. Heck I idle at 15-20PSI whereas the base kit idles at I think 30PSI or there abouts.



I used to race cars, now I race myself.
5K PB: 24:50
10K PB: 54:26
Re: Boost loss with stock exhaust
Wednesday, March 22, 2006 12:27 PM
Stock exhaust will limit how much boost you can build.

For example:

Tom's car w/ full stock exhaust would only hit 10psi or so..... but with the cut-out open, could hit 18+

My buddy with a VR6 could only hit 6pis on his w/ full stock exhaust (10psi spring), with larger exhaust, he hits 10psi no problem.

BACK PRESSURE will limit your ability to build boost.




SPD RCR Z - '02 Z24 420whp
SLO GOAT - '04 GTO 305whp
W41 BOI - '78 Buick Opel Isuzu W41 Swap

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