So I was working on the car today, put in turbo timer, and a boost gauge. i took it for a spin when done and with the stock actuator it would only max out at 14 psi, idles at 16-18 vac, put wou;d max at 14 psi and not taper, mods are br tbe, k&n drop in, and br ic, still has crappy stock bov, have been thinking it might be leakign cause it has felt like the car has been slower lately, would that cause it to not hold enough boost? i had an mbc laying around the garage from an old project that didn't get finished(brother totaled my other car) and so i put it in, and couldn't get more than 12psi out of it, any ideas? I think the MBC was crappy to begin with, but it had never been used before, what do you guys think.

 

How did you have the MBC installed?

 

tee'd the BOV line to the waste gate like the write ups all show, had one question was the turbo outlet line you are supposed to cap the one that was on the stock lower intercooler piping because i couldn't find what they were refering too, that was my only question on the install

 

Mike @ Forge:

"Turbo Outlet

This is the standard method of connecting a boost controller and arguably the safest.

If there were no boost controller at all being used in the system, this is the method REQUIRED to be used.

Without a boost controller, you ONLY want positive pressure acting on the diaphragm of the actuator. NOT pressure and vaccum as would occur when connecting the source to the inake manifold. The vacuum can pull on the diaphragm of the actuator pulling it into the unit's vacuum nipple and potentially tear it.

When a boost controller is used, this is not an issue as the vacuum is pulling on the ball of the boost controller instead of the diaphragm of the actuator.

(this is only the case for a lock-ball and spring type manual controller)

This also allows the boost controller and blow-off/bypass valve to have their own references improving the response of each individually.

Intake Manifold/Sharing with BOV

Sourcing the reference from here MAY provide a very slight improvement in repeatability of boost, however, this is a less safe method of installing the boost controller and actually leads to another issue that can hinder the performance of the car.

First and foremost, the Bypass/Blow-off valve must always have a intake manifold reference. NEVER reference the valve from the turbo outlet. Please don't confuse that with what I am refering to here.

If the boost controller and BOV share that same reference from the intake manifold, they are essentially sharing the same volume of air (pressure/vacuum).

When the boost controller (lock-ball-and-spring type) actuates, meaning when the spring allows the ball to come off of it's seat and send the pressure signal to the actuator, some of the "shared" pressure helping to hold the bypass/blow-off valve closed under boost is now momentarily diverted to the wastegate actuator potentially causing a "flutter" in the seal of the bypass valve and a slight loss of boost pressure altogether within the system.

If the boost controller and BOV each have their own individual reference from the intake manifold, the possibility for this flutter is greatly decreased, however, it may still exsist to some extent because both references are sharing the intake manifold pressure.

Al and I have seen this issue on mutiple vehicles and sourcing the boost controller directly from the turbo eliminates it completely.

In short, the best method will be connecting the boost controller directly off of the turbo outlet or anywhere on the intercooler piping BEFORE the throttle body.

Boost Controller
Positive Pressure Only
(Turbo Outlet)

Bypass/Blow-Off Valve
Positive Pressure AND Vacuum
(Intake Manifold)"