lower boost than expected?

[dzcook98]

Hey, so I recently installed a boost gauge on my project car. Its a 2001 Pontiac Firebird with an L32 supercharged series III in her. Runs just fine for the most part, but I'm not making anywhere near the boost that I thought I would be making. It's on the stock supercharger pulley, and I was expecting to get somewhere around 5 psi - compared to the 7.5 that the fwd supercharged 3800's make. I only topped out at 2 psi - occasionally hitting 3.

I am on some NGK TR6's, and zzp told me to swap them out for some Autolite 104's. Could the colder plugs be effecting the boost levels?

Thanks

[ssms5411]

No , I don’t see plugs having anything to do with boost levels. I like the TR6’s. Been using them when I had a super charger, nitrous and turbo. And will use them when the turbo goes back on. I would look elsewhere,

[mdiesel]

sounds like you might have a vacuum leak somewhere..check your vacuum lines, then look for leaks at the intake.. somewhere your loosing pressure it sounds like anyways

[ssms5411]

Most boost gauges do vacuum and you should be 20-22 vac.

[LETZRIDE]

Are you running an intercooler? I remember hearing those folks running an intercooler would drop psi in the fwd cars.

If not that, I would definitely look for a vacuum leak like stated above.

[dzcook98]

No intercooler, mostly everything is stock except for: headers, drop in air filter, 180° tsat, and a tune for 93.

I average about -8 vacuum when at idle, -11 or so on hard braking. Only ever seen it hit 3 psi like 2x since the install.

Reason I thought plugs might be the issue is because there is a dead spot in the rpm range from 5-6k where the power dies off and it kinda sounds like the motor is stuttering. It was a mistake, but we forgot to gap the TR6'S to .055 before installing, so I thought maybe that might be some KR at the top end of the power band, thus why I'm not making the boost I should be.

Will look for a vacuum leak soon. Thanks guys!

[ssms5411]

I’d leave the TR6s at what they came at .035. You probably have a vacuum leak if your only at 8-11 vac.

[ssms5411]

Vacuum leak will make it run bad , you’ll get misfires and overall run like crap.

[dzcook98]

Okay thanks! I'll be sure to try and find the leak, appreciate the advice.

[LETZRIDE]

This might help you if you arent sure on how to start testing for boost leaks:

How to test for boost leaks

[dzcook98]

Hey guys, so I checked the vac lines. No leaks to be seen. The waste gate is stuck open from what we could tell thoughts that we've been tossing around:

We did not plug in the boost solenoid - as suggested by Intense Racing. Is it possible that since it's not plugged in, then I am not getting my full boost? I'd have to find a way to pin it into my L36 computer, so that it only activates when I need it and not all the time.

Or

Someone suggested that maybe the diaphragm in the wastegate is bad?

Any other ideas as to why I'm getting such low boost?

Thanks

[ssms5411]

Yeah if the diaphragm is bad I’m surprised your making any boost. Is there a way of running aftermarket wastegate ?

[mdiesel]

im no expert on this, but the m90 is a roots style supercharger. do you even need a waste gate ? I mean look at a 671 weind blower for an old school carbed motor, no waste gate there. I was under the impression the waste gate on the m90 was simply to lower boost in certain conditions, like extreme kr...

[dzcook98]

I did a quick search about aftermarket wastegates for the M90, only think that came up was external ones from a turbo kit, and that won't work. Could do an oem replacement of the waste gate if the one I have is faulty.

in regards to whether it is really needed or not, I can't say for sure. I'm no expert either, this is my first experience with boost of any kind. From what I understood, or have been told - the waste gate is controlled by the boost solenoid? But Intense and everyone I've talked to about this says that the solenoid does not need to be plugged in and is only activated when it sense overboosting, but since this is a roots style blower, it can only spin as fast as the motor allows it to spin.

I guess that's where the confusion is lying rn. Does the solenoid need plugged in to get full boost? or is there something else wrong. I installed a 3.6" over the weekend that was supposed to take me to 9-10 psi, but I'm still only at 2-3 psi.

[ssms5411]

What would happen if you bypass the one on their now? Might try it and see what psi it goes to.