legacycentral bbs

My 92 legacy ss has a hallman MBC and forge BPV, wrx cold air setup (fender snorkel). Recently, i've noticed that the boost has gotten lower and lower on my Lamco gauge, when i got the car, the seller claimed he had it set of 13psi, but when i drove it, the gauge was only reading about 0.04 MPa, MAX. Which is something like 7psi?.. Anyhow, recently I've noticed it is only reading 0.03MPa, or about 5psi..

I wondered if my MBC was hooked up correctly, so i messed around, i found that the jam nut wasn't snug, so i naturally backed off the MBC all the way, ran the same boost, 0.03MPa.. Stop, crack jam nut loose, turn the MBC a bunch of turns in, started to feel some tension in the knob, figured that was the norm, so i tightened it back up and took it for a drive

I think i may have noticed a slightly more responsive boost, but again, 0.03MPa on the lamco gauge.

At this point i've stopped adjusting it, and i will probably investigate and insure that the factory solenoid isn't connected to anything and that the manifold-boost source is going into the bottom of my MBC and that the side nipple leads to my WG actuator.

I did however, notice that the compressor housing nipple had a hose on it still, so i will have to double check everything tomorrow..

I just don't want to find out that something is terminally wrong with my turbo, it's got 325,000 km on the car, doesn't make any bizzare noises, no screaming BOEING 747 noises from boost leaks under WOT, nuffin!

Also is it possible that my forge BPV is bleeding/recirc'ing boost and that is where it is being lost?

Thanks for the time guys.

stock turbo or aftermarket? The wastegate move freely? You might try tightening the MBC more -- could be the spring has gotten weak over time (this happened with mine).

Stock turbo, also, he has the compressor nipple and the manifold going into a T fitting as the boost source for the mbc, and the oem boost solenoid is infact disconnected

update, i cranked up the mbc, finally got it to make some boost, it spiked at .1mpa, popped off the compressor/boost source line, stopped and plugged it back in, and turned down the mbc.. later tonight i hit fuel cut while pulling 50% ish throttle uphill in 5th, so needless to say, time to back off the mbc again and reset the ecu by pulling the EFI fuse.

Can you go into a little more detail on how the MBC is setup.

The way it should be setup is the vacuum/boost fitting on the compressor side of the turbo should go directly to the inlet of the MBC. There shouldn't really be any tee's in this line. The oulet line from the MBC should go directly to the wastegate solenoid fitting.

If you have anything other than that setup, you should redo the vacuum lines.

The MBC is using both of the recommended boost sources, so it has a line coming off the intake manifold (which i read is the source that is suggested to be the best) and a line that comes off the compressor housing nipple.. These lines join at a T fitting, and then go towards the MBC inlet.

The MBC outlet line goes to the wastegate actuator.

Sorry for the late reply, but you do not want to setup your MBC like that. You want to hook it up like I mentioned in my previous post.

With those two lines teed together you are creating a path for higher pressurized air from the compressor to bleed off into the intake manifold. This can create boost spikes as well as slow down turbo spool. You are always going to have a pressure difference between the turbo outlet on the compressor side and the intake manifold. You want to use the turbo compressor outlet as your boost reference source to minmize/eliminate part throttle full boost situations.