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Exhaust gas behind intake valves

Engine Building Fundamentals

Discussion and questions related to the course Engine Building Fundamentals


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I had my head off and noticed dirt on the intake port which looks like exhaust residue. Did some googling and found a term for this I believe "reversion".

It's present on all the ports, I run an aftermarket cam but it's not aggressive. This can't be good for performance, is the cam opening the intakes too early?

Here is a picture, everything above the green line should be bright silver.

This is a jetski motor.

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Looks pretty normal to me. Your intake system, exhaust system, cam timing etc are all part of wave tuning. At one specific RPM they will all work in harmony and you will get the best cylinder filling, but at all other RPM's either side of that sweet spot there will be compromises. Intake reversion and EGR are part of that.

Ah ok thank you :)