Pot scourers got mine down to 83 db @ 3500 rpm.
With the scourers removed if you get on the right pedal they are noisy but not offensive.
2 1/4" stainless spiral louvered tube 25" long with a layer of S Steel wire wool and a few layers of "E glass" matting behind packed tight gives a great mellow sound.
The outer shell of the muffler section has an air gap and the muffler slides into the 3 1/2" section of the pipe, the muffler section is warm but touchable after a drive.
http://www.youtube.com/watch?v=t_0-5lvAo-I