Good day all.

I'm looking for advice on an exhaust design problem. It is easy to find videos explaining exhaust scavenging, but how do you control it? Surely there must be some physics that can be applied in order to design a header that targets a specific RPM range for exhaust scavenging to improve torque?

Can it effectively be done? If so, are there good and bad examples?

Would it negatively affect the spooling of a turbo?


  • There are similar questions on here, worth a search.
    – Solar Mike
    Commented Aug 6, 2020 at 4:57
  • I've taken a look at the similar questions and read the other questions. I understand the concepts, they're relatively simple. I'm looking for the next level. Perhaps I was unclear, but I'm looking for formulas and scientific background for how to design an exhaust system for performance at specific RPMs.
    – Laine
    Commented Aug 7, 2020 at 12:40
  • Then you should have found my reference to David Vizzard and Mini tuning - a good start as he details making a flow bench to test heads..
    – Solar Mike
    Commented Aug 7, 2020 at 16:01
  • A formula would be the holy grail of stuff like this. Designs like this are done with simulations. This is because there are far too many variables that can be stuffed into a simple formula, engines are far too dynamic. Pre turbo scavenging is basically a waste of time. The pre-turbo back pressure will dominate negating any kind of scavenging effect. Runner diameter can be optimized for increased velocity and runner length can be optimized so that exhaust pulses arrive at a particular time but that is about it. All the work is done post-turbo to reduce backpressure.
    – vini_i
    Commented Aug 7, 2020 at 19:20
  • To my knowledge, scavaging is about timing of exhaust pulses in relation to each other rather than a specific speed. Scavaging relies on one exhaust pulse pulling the next exhaust pulse. It doesn't matter if the engine is running at 600 or 6000 rpm for this to happen. Also, when considering turbocharging, scavaging doesn't matter. It will be overridden by back pressure in the system as the exhaust gasses stack up behind the turbo. Commented Apr 7, 2021 at 17:40


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