Automotive Muffler design
I've found a little bit of this discussed but not as in depth as I'd like to know.
For discussion purposes I'll be referring to my experiences with common aftermarket sportbike mufflers from the likes of Yoshimura, Akrapovic, M4, Scorpion, yada yada yada, there are literally 50 or more makers. All have a perforated, many small holes but smooth surface, core wrapped with an absorbing material like fiberglass, expanding foam or a twine like material. The inside diameter of the core is rather large, at least 1/2" to 1" larger than the pipe size feeding it but tapering back down at the exit end to squeeze the exhaust pulse into the muffler packing I assume. This type of muffler is used in racing and provides the least amount of restriction I am aware of.
What has changed over the years and made these mufflers quieter is the outer shape/cross section of the muffler body from Round to Oval to Tri-Oval to now I've seen some non-symmetrical ovaled megaphone shapes. It would seem that doing away with symetry is good for cancelling sound waves just like when designing an enclosure. With the muffler, making the sound waves travel longer distances and thru more of the the damping material via odd reflective surfaces before they return to the core and exit.
- A round muffler body will reflect sound back to the core so the sound wave travels thru the material twice, once on its way to the inside wall of the body and once back to the core.
- An oval only has this direct reflection 4 places at say 12, 3, 6 and 9 o'clock, the rest will reflect the sound wave back to the core in an indirect path thru more of the damping material.
- More so with a Tri-Oval and even more so with this new teardrop oval megaphone shaped muffler which is not parallel to the core at any point.
My question is what muffler body shape will absorb or muffle the most sound or is it rather a function of having the least amount of symmetry/parallel-ness etc. ? Is there more to why these mufflers quiet the sound than I'm aware of?
I'd also like to discuss why or how a "FlowMaster" style of muffler sounds the way it does and what all is going on with its many baffles/chambers etc.
Last edited by 901Fixer; 21st September 2009 at 05:01 PM.
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