Quote:
Originally Posted by Thumper
"The PowerBomb is a “pre-muffler” of sorts which helps to lower the bikes sound output by providing more sound absorbing surface area for the sound medium (exhaust gases)."
This is what they say. FMF doesn't call it an expansion chamber. They mention sound reduction and power increase, but without calling it an expansion chamber. But all of the 2-stroke pipes have integrated full expansion chambers. Maybe this is semantics, but a 4 cycle engine can't benefit from the classic expansion chamber, or they would make pipes with them for 4 stroke bikes.
An expansion chamber is different:
"The basic idea behind an expansion chamber is to use the momentum and pressure of the exhaust gases to create a pump that squeezes more air and fuel into the cylinder during the intake stroke. It does the same sort of thing that a turbocharger does, but it does it without moving parts."
A collector in a multi-cylinder 4-sroke exhaust system is related. The collector is at the union of the headpipes, but before the muffler (which can be a megaphone, which IS in fact an expansion chamber of sorts). Pulses are "tuned" at the collector to create a vacuum following each pulse. This creates an extraction effect, sucking more gases out of the cylinder during the exhaust stroke, and allowing more gases in on the intake stroke. It is also NOT an expansion chamber.
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Sounds more like a resonator than tuned length headers or an x-pipe.
Which effectively has no effect other than changing exhaust note.
That makes sense.