hy do MBCs bleed off boost

[notractiongst]

Im just curious as to why MBCs bleed off excess boost .. wouldnt that be a boost leak pretty much since the MAS has already counted the air ??? i just dont understand why they bleed of boost

 

[steve]

What makes you think a typical MBC bleeds off boost?
The usually block the boost from reaching the wastegate actuator until they open.
Once they open the vent may leak some air untill the boost falls off but that's not why it's there. It's intended to vent and trapped air between the valve and the WGA so that the WGA can close once the pressure drops. Otherwise the WGA would stay open after the first time the boost exceeded the MBC setting and you'd never build much boost again. The vent should be tiny and not leak enough air to effect metering.

Steve

 

[notractiongst]

oh i was just curious cause it seemed like mine was leaking a whole buttload while i was doing a boost leak test.. i forgot to tighten it all the way down