[Archertsi]

Ha, this is a great topic. I have experimented with this myself. I do believe the bleed hole on each MBC is drilled to a correct size to keep a certain ratio with it's inlet/outlet port. But I also think it can vary with each cars set up. Different size vacuum hoses, the size of the hose barb fitting supplying boost to the controller, the hose barb on the wastegate, etc.

On my friends first gen with a E316g (stock WG flapper and actuator) we have been trying to solve boost issues. The car builds 30psi no problem, but tapers down to 23-25 psi by the end of the gear. We read about different theories like the wastegate being blown open causing it to taper off. Or that the turbo could be spiking the boost until the wastegate catches up.

Either way, we had to test to try and figure out what it was. My theory was that the boost was spiking to 30, and then tapering back to what the MBC is actually set to (23-25 psi) because the WG was opening too late. If you look at the boost inlet port on the MBC, there is a restrictor, the hole in the center is very small. By enlarging this hole, this allows more air to push on the ball and WG diaphragm, sooner . The down side is the additional air cannot be bled off through the stock size bleed hole. So when boost drops down, (WG open) it takes a little longer for the WG to close and raise boost back up.

So by enlarging the bleed hole (along with the hole in the inlet port) we allow more air to actuator sooner so it can work faster, opening the WG sooner and preventing a spike. No spike allows you to raise the pressure that the MBC is set to. But the holes need to be drilled in the correct ratio to each other.

Instead of 30psi tapering down to 23 where your MBC is actually set to, you set the MBC to 30 and leave it there. Testing what pressure your MBC is actually at can be verified with compressed air and a regualtor hooked up to the inlet port of the MBC.

The testing we have done so far has not yielded success yet (remember, these theories are just what we think)

Another thought I have yet to test is a WG actuator with a softer spring. A softer spring would take less air to open the WG acurately.

Think about it, for years people have stiffened WG springs to prevent them from opening early. But you loose some control that way.


Kracka, you asked if you get more lag. Well yes, you may. But to hold high boost through gears like 3rd, 4th and 5th is probably more worth it IMO.

Just my thoughts on the subject but I think this thread could lead to some great brain storming for those who are open minded enough and fully understand the theory of an MBC.