4 stroke exhaust

This is a silly question but if you ride a 4 stroke single, I notice when idling, the exhaust pulses bounce all over the place behind the bike. Why not a straight pattern? It's weird.

Its an attempt two confuse 2stroke guys that they are surrounded

budzrex said:

Its an attempt two confuse 2stroke guys that they are surrounded

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Good option!

Could be that each pulse is affected by the disturbed air left behind by the previous stroke. That's just a wild guess.

I believe it is the harmonic frequency of the large-ish piston that is affecting the "vibrating" exhaust. One a large displacement twin engine, it is easier to see how the entire motorcycle is affected by the harmonic vibrations traveling through the bike at idle. In the thumper the harmonic frequency is present and vibrating the entire motorcycle, but it is less perceptible to the eye.

Take this with a big grain of salt:

I believe that the pulses traveling through the muffler and baffles will create *relative* areas of high and low pressure within the muffler itself, so each next pulse will take a slightly different path than the previous (follow the low pressure)... so when a pulse gets to the end of the muffler, it is not always pointing in exactly the same direction.

Kinda like this if you picture each path as an individual pulse:




... of course, i could be totally dead wrong on this one.

Not something I've ever noticed riding behind anyone or off the mufflers of my bikes. They have factory exhausts that are very consistent.

Probably only bikes that aren't restricted.