Road and Race

[DukeRed]

So what's the difference between a race and a road can? Is the internals of the can actually different? Is it just the dB level that's different?

Jan
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[Frost]

race cans offer increased power over road cans due to the design. To increase the power the exaust gases are allowed to flow much more freely without scilencing of baffling. this causes race cans to be louder.

[mchaggis]

I'll desist from the whole essay on exhaust configurations for just now... Race pipes tend to be straight through pipes, with the focus on developing the most power rather than noise control.

I'm not sure which type of silencing race bikes will use, I imagine only multi-resonant silencers though, and probably only single pass at that. That is to say, the main pipe goes in a straight line through the muffler, and the chambers inside the muffler won't have anything in bar air.

On a normal road silencer, it is quite likely to be three-pass multi-resonant, with the chambers containing an acoustically dead material, such as rock wool, or glass fibre. This fibre absorbs high frequency sound from the main pipe (the main pipe is comprehensively perforated) as the sound forces this fibre to vibrate. The three-pass part means that the pipes inside the muffler pass through it effectively three times, doubling back on itself twice inside. This lets you fit a lot longer exhaust system into a lot smaller space.

The three-pass and the resonant and absorbant chambers are what loses you the most power, as the exhaust gas is slowed down, and the back pressure increased (the engine having to do more work to push the gas out), by both the increased length of the system, but also the exhaust gases losing energy meandering about in this fibre stuff. That said, they are much better at cutting noise pollution, which is more important on the road imho.

(If you want me to try and explain the principle behind the Helmholtz multi-resonant chambers, just say so... )