So heres the deal

95GSTRaCeR · #1 02-03-2004, 05:27 PM

I have a 95 GST with a 14B setup, ebay mbc, walbro 255, and an HKS SSQV. My question is if i'm not leaking any boost what else could be limiting my boost to stock? Do I need anything else besides an MBC to up my boost. I've been trying to get my boost higher and nothing is working. I made the boost leak tester on VFAQ and tested it, fixed all the leaks, and still nothing!!

any help or input will be appreciated!!

BoostedSpyder · #2 02-03-2004, 05:36 PM

stock like 15psi? i'm assuming you have a boost gauge. throw the mbc all the way up. if that doesn't do anything throw it away and get a new one, not from ebay.

95GSTRaCeR · #3 02-03-2004, 05:39 PM

I'm sorry, didn't exactly clarify "stock", i've always been told stock was around 8 psi and that is what i'm boosting. I took the mbc off and tested it seperate with a air pressure guage and a compressor. It was working properly, but even with it off and the stock setup shouldnt I be boosting 15 psi, if that is stock?

BoostedSpyder · #4 02-03-2004, 05:46 PM

stock on a t-25. are you able to adjust the mbc at all? 8psi seems low.

95GSTRaCeR · #5 02-03-2004, 05:54 PM

I can adjust the MBC, but even with it cranked up all the way it still wont boost any higher. Is there maybe something that can be drawing the pressure out of the intake or anything like that? (this was a suggestion from a friend). Also when I hit the gas, boost, and let off, the car will sometimes shut off, it seems to happen mostly when i step on the brake. The person that said that something may be drawing the pressure out said that he thinks my brake booster is what is causing my psi to be only stock and that is why my car is dying when i stop. any idea if this could be a possibility?

BoostedSpyder · #6 02-03-2004, 06:11 PM

you aren't recirculating your BOV, and that could have something to do with your idle problems. it seems as though your wastegate is opening prematurely. you could have some lines crossed somewhere.

95GSTRaCeR · #7 02-03-2004, 06:33 PM

if i have an mbc in there shouldnt i be able to hold the boost before it gets to the wastegate actuator?

BoostedSpyder · #8 02-03-2004, 06:39 PM

exactly. you are on the right track.

95GSTRaCeR · #9 02-03-2004, 06:44 PM

im pretty sure i have the mbc hooked up right but just incase... i have one line T'd into the line running to the BOV nipple, and the other line T'd into the line running into the wastegate actuator... is this right? I now that the lines that run into the MBC are going in the right ways but maybe the others aren't? Just an idea...

95GSTRaCeR · #10 02-03-2004, 10:39 PM

could i be losing boost dumping to atmosphere? or is it not that significant?

JoeWagon · #11 02-03-2004, 11:10 PM

you don't lose boost through dumping.
Either you have a boost leak in the BOV, or you don't.

And, the only thing that should happen when you vent/dump to atmosphere is crappy idle, and similar problems when you DO dump, as in let off the clutch.

kjewer1 · #12 02-04-2004, 03:58 AM

8 psi is in the normal range for a 14b actuator. The t25 is around the same psi, but the ECU brings it up to 14-15 psi

The brake boost is out of left field.

I would disconnect the line from the actuator and cap it off (the line, not the actuator). Go and flooor it. Be ready to lift quickly though, if your WG is working and everything else is in order you should get unlimited boost. If you do, then its the MBC. If you still get low boost, its something else. Such as:

-flapper isnt seated (adjust preload on actuator arm)
-actuator is banjaxed
-WG flapper is not centered over hole (common on old turbine housings)

95GSTRaCeR · #13 02-04-2004, 09:55 PM

I plugged the actuator hose and my boost would fluctuate between 7-15 psi rapidly, it boosted smoothly until it hit 7. Could this be because the flapper is not seating tight and shaking around? or maybe ignition related?

95GSTRaCeR · #14 02-05-2004, 03:48 PM

How do I adjust the preload on the actuator arm?

kjewer1 · #15 02-05-2004, 11:16 PM

REmove the pin from the actuator arm, and remove it from the flapper arm. Hold it up to the peg it sits on on the flapper arm. The actuator should seem a little too "short" to reach. Requiring a bit of stretching to get it over that peg. That preloads it properly. Dont preload it too much though, or you lose travel and boost creep will go up. There is always a compromise

And this is much easier with the turbo off the car.

More likely the flapper is not centered. The flapper arm protrudes from the turbine housing just 1/16th or 1/8th of an inch. If there is a lot of that bushing and flapper arm hanging out of the turbine housing, you can be pretty sure its not centered. Check that out and let me know what you think.

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