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Old 08-25-2022, 04:10 AM   #12 (permalink)
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Originally Posted by Ecky View Post
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.
Tuned length exhausts and how they provide low pressure at cylinder during the exhaust stroke at a pre defined rpm is a whole different subject Ecky.
Here I'm talking 'Overall, at any RPM' on a stock untuned manifold.

I do have a post in the making on them (calculators and all)
Anti Reversion 'valves'
(Reduce backward flow below the branch's defined rpms)
Pressure Wave Termination Boxes
(makes the last 'into one' pipe also tuned, the rest of the system 'invisible' and has anti reversion)

These all reduce the 'exhaust into the intake tract' EGR during valve overlap you mention.
IMHO that's only better for reducing NOx emissions but does little for economy.

As you seem into all this; Have you looked at Koenigseg's Freevalve tech?
~3X the power/economy! IIRC
He wants to connect the valves to an A.I. and see what it comes up with!

Last edited by Logic; 08-25-2022 at 06:57 AM..
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