How far do you want to get in to this here? It's really quite a science. Would it help to offer that a wrap around Pitts is quieter than a stock muffler, a wrap around Pitts with an oversize can section will be quieter yet, a header/can arrangement might be even quieter, and if you'd like to spend the money, you can make it quiet and pick up some power with a header/tuned pipe arrangement?

The why's and how's on the tuned pipe arrangement would fill a book. Should really be approached, I think, by guys really into that kind of thing, with the time and patience to sit down and figure it out, then spend some time (maybe a lot of time) experimenting with the engine they're interested in messing with. There's a lot to it, and much to be gained.