How does exhaust length change the powerband?

So since I’ve been driving X30, I’ve heard repeatedly from different drivers about how shortening my exhaust will give me more top end, or how lengthening it would give me more on the bottom end.

I’m using this season to learn more technically about my engine, but this one confuses me. Can someone explain to me how this works?

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Basically there’s a sound wave in each pulse that returns back up the exhaust pipe, towards the exhaust port.

When the ports open in the cylinder, some of the fresh charge can exit the exhaust port.

This pulse can be used to keep that charge in the cylinder.

Changing the length of the exhaust influences the time it takes for that wave to travel back to the exhaust port.


So real simply, the shape of the thing knocks exhaust back towards the cylinder? It is timed in such a way that the returning wave of pressure meets the opening on the piston port (which is open to the exhaust system at that point in the stroke) and prevents the air/fuel mix that has just been squirted into the cylinder from escaping out the port? Sort of like an invisible wall?

I always have run minimum length in X30. There’s almost never a need to change it. If you’re looking for less peaky power, you can lengthen it to spread the curve out over a wider RPM range, but I’ve never found that to be better for X30. It already has good mid-range. Even on the Leopards which were more top-end biased, lengthening the flex usually hurt us more than helped. Because you flatten the power curve, you lose the big kick of power and it makes the engine difficult to race. Your lap time might be the same but we always found a longer flex made you a sitting duck in traffic.

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I don’ know if this will help or make it worse, but this guy on Youtube has some pretty good videos that might help

There are some good animations of what happens during the combustion cycle, and also has a video specific to the KA100.