legacycentral bbs

I installed the Hallman Pro RX MBC on my 91 SS. With the soft spring I can run about 10psi...with the stiff spring...it only runs 10 psi as well...all the way cranked down.....

I am stock all around....what are results of others using similar MBC's?

I was thinking that maybe the exhaust is limiting the boost

disconnect the wastegate and see if you can get more boost without it, but only for a split second. With my mbc and a 16G turbo I could never get more than 15psi in first and second gear even after I disconnected the wastegate.

How have you hooked up the boost controller?

The bottom tube I spliced into the line coming off the intake manifold...the side tube to the wastegate....capped off the turbo nipple.....that's it

it definitely works....but can't go over 10psi

Should work. I have a Hallman, I think the exact same model, and I was up at 12-13psi no prob.

As a separate issue: Don't plumb it off the intake manifold, plumb it from the compressor to the MBC to the wastegate. That way you won't overboost the turbo at part throttle. Doesn't answer your question, though.

You mean from the turbo to the MBC to the wastegate?

macipusy wrote:You mean from the turbo to the MBC to the wastegate?

Yes.

yes, the nipple on the compressor side of the turbo

Not familar with the hallman, but if there is no bleed/vent of air you will not be able to increase boost (MBC's are just adjustable boost leaks).
If there are just 2 fitting on your MBC with no vent on its body then 1 of the fittings is the vent.

I have a cheap-o e-bay MBC in the LSS at the moment & I "T'd" 1 fitting into the line going to the wastgate, the other fitting was left disconnected (or connected to the coffee-mug) as it is the vent that allows you to raise boost.

Nope. Disregard what BXSS said. He is correctly speaking about one type of MBC, but it's just that he doesn't understand how a ball-and-spring MBC works.