Herb Sanders wrote:

Paul, someone mentioned some Russian research that indicated square
pipes were effective at noise suppression in exhaust systems. Do you
know if this is fact or fiction?

 Herb, I once built an expansion chamber exhaust system for a 2-stroke kart
engine that was fabricated from flat .035 mild sheet steel pannels. It
looked like a microwave or acoustic horn. I thought it might be an
alternative to rolled cones and cut lap times too!
 WRONG
Lost performance, lost reliability (flat areas vibrated and cracked), and
LOUDER than hell! The flat surface area vibrated like a drum head.
 The first Yamaha TZ 750 roadrace bikes had a similar problem. Don't
underestimate the values of  round sections and compound curves.

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