Posted by William Boylan on March 18, 2002 at 04:38:10:
In Reply to: Muffler Comments, Please: posted by Hal Pollner on March 15, 2002 at 16:46:16:
I recently purchased an "as new" muffler on E-Bay. I happened to notice that the exit hole in the muffler was smaller than on the one I was replacing. The old mufler measured 7/8 inches and the new one was only 3/4. Hmm... what to do. I had the head-pipe out of the head so I measured the ID of the "Inner" pipe at the head. It measures 1.30". What gives? A bit of the ol' "pie R Square" will tell us that a 1.3" diameter circle has a bit more than 1.3 sq. in. area while a 3/4 inch diameter circle has a bit less than 1/2 sq. in area. (Believe it.. do the math) That is one hell of a lot of difference. Is that much back pressure necessary? With just a bit more math I find that by drilling 8 ea. 3/8 inch holes around the exit hole in the muffler I end up with almost exactly 1.3 sq. inches of exit, the same as the "inner pipe" at the head. Well, guess what, the bike seems to run just fine and noticably stronger. She barks a bit, but not too bad. A bit higher pitch, at idle, than I would like, but sounds pretty good on the road. Hope I didn't screw something up. Any comments?