Quote:
Originally Posted by CobraMarty
So at low rpm there is more vacuum where there is low flow/velocity. At high rpm there is less vacuum where there is high flow/velocity.
I'm not so sure what this really means. Is the vacuum dropping because the air velocity is raising?
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No, it has nothing to do with velocity really. Nominal atmospheric pressure (on Earth) is 1-bar / 100kpa / 1000mbar /14.7psi (with differences for elevation of course). The N52 normally opens the throttle all the way (except for special circumstances like overrun or idle), so theoretically the manifold pressure should always be 1bar.
When you start to see manifold pressure drop, that means that something is restricting air from entering the manifold and keeping pressure inside equal to atmospheric.
You'd see the same thing on a traditional throttle based engine, where the throttle itself is the "something" that restricts airflow - the more closed the throttle, the higher the vacuum / lower manifold pressure, the more open the throttle, the lower the vacuum / higher manifold pressure. Since the N52 nearly always opens the throttle to 100%, manifold pressure should always (theoretically) be equal to atmospheric.
All in all a 5% pumping loss near redline isn't bad but it does mean that there's some small potential to improve on it. The trick would be figuring out what is the source of the largest restriction (throttle? airbox? maf? the manifold itself?).