" Tuned Pipes - Or how the Resonance Effect is affecting Performance"

We all know that the exhaust pipe and the length of the manifold have an
effect on our engine's power output, but how exactly does it work?

First, imagine an engine with all ports, like the one below:

In our two-stroke engines, the intake port and the exhaust port are open at the same time. This means that the amount of fresh mixture that can be trapped in the combustion chamber is limited. An engine produces the more power the more fuel/air mixture detonates.

Thus, our goal is to increase the amount of fresh mixture burnt during each cycle.
To do so, we need something that prevents the fresh mixture from leaving the
combustion chamber unburnt.

Have a look at the animation on the left. You see that the burnt exhaust gases form a pressure wave which goes to the end of the pipe (or the baffle), then reverses direction and prevents the fresh mixture from leaving the combustion chamber. This walve is called back pressure.

So, knowing all this, how can I improve my buggy engine's performance?

What you can do to tune the exhaust system to your liking is to change the
length of the exhaust (distance from engine's exhaust port to pipe's baffle).
You can normally tune that by adjusting the length of the coupler (connecting
tube between manifold and pipe). Making it longer means that the pressure
wave takes longer to come back. The result is better performance at low revs,
that's more bottom end, acceleration. Having a shorter exhaust means that
the pressure wave is back faster, so you have the resonance effect in the high
revs. The result is additional top speed.

I'm not sure how often this adjustment is used in 1/8 buggy racing, but RC
helicopter pilots use the resonance effect to get more constant rotor revs
without using a governor.

Have fun racing, bashing, or just wrenching!

Greetings, Thomas

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