Quote:
Originally Posted by Logic
but
In a stock, cast iron manifold, I think the drop in exhaust gas volume leads to less restriction/back pressure and thats where a lot of the extra power/economy came from?
I know whats going to happen:
Someone's going to jump on here saying "more exhaust gas speed = lower pressure".
Well then; why don't we all make our exhaust systems the diameter of a drinking straw??
ie: Lets avoid quoting the venturi effect out of context...
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You're right in that there is a bit more to it. Exhausts tend to have their scavenging tuned for a rather specific RPM range, where the pulses are timed to create suction that more fully evacuates the cylinders. Exhaust scavenging is actually counterproductive for economy though because often you
want exhaust gas recirculation - though that can be controlled by cam phasing (VVT).
I'd say it's probably too complex to generalize about.