Smaller pipes will create higher velocity in the exhaust system, but the placement of the muffler(s) is the critical factor. Low-restriction mufflers close to the engine and a long tailpipe will allow for more resonance. I've got a cure for loud pipes- - - -it involves a good bench rest and an accurate rifle!
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!