Let me preface this by saying that I've done a lot of searches.. and haven't found an answer. If it's somewhere already on the board, kindly point me in the right directly.

I just installed my MBC and it seems to hold boost at 20 psi until around 6K rpms where it tapers slightly to about 18 or so. Is this normal behavior?

 

I know i have been told before that MBCs do tend to not hold boost like a EBC. but i would think that it would be normal for it to taper a bit even woth the MBC or EBC just because it is probably alot safer for the turbo

 

An MBC will have a tendency to fall off at higher rpms, that is a characteristic of the design. An MBC can only hold pressure back from the wastegate diaphragm for so long, then all the pressure goes and undoubtedly some will allow the wastegate to stay open longer than it needs to. The MBC merely controls characteristics of the wastegate known as accumulation and blowdown. The EBC will likely hold better because it will see the change in boost and adjust accordingly.