View Single Post
      10-21-2012, 01:57 AM   #14
First Lieutenant
CarbonFoot's Avatar

Drives: 2017 F80 M3 DCT ZCP
Join Date: Dec 2011
Location: CA - Bay Area

iTrader: (2)

Originally Posted by pbonsalb View Post
On a boosted motor, boost is a measure of the restriction through the motor. Take the cork out of the backside and boost drops on a supercharged engine.
Can you expand on this statement? I don't see a strong correlation between boost pressure and exhaust restriction. While, of course, a high flowing intake and exhaust should be well matched to produce good power, I see them as separate functions.

As I see it; when boost is created, it pressurizes against a closed exhaust valve during the intake stroke. During the exhaust stroke the intake valves remain closed until just past TDC. I can't imagine a lot of blow-by is occurring in the cylinders under boost, where the supercharger is pressurizing against a restrictive exhaust. Exhaust pressure is generated by the compressive force of the exhaust stroke and not the intake system.

That being said, I don't see how uncorking the exhaust will lower boost.

Please correct me if I'm wrong as I don't know much about actions of vanos and the resultant effects it may have on this.