If you're running a turbo you shouldn't need a muffler. The turbo serves the purpose of the muffler.
Mark
A turbo helps, but listen on this video to my 20B and Dave’s 13b turbo, and Mike’s 13B NA with some other kind of muffler.
http://www.youtube.com/watch?v=dibuqenWcOk
(Courtesy of Paul Lamar. He did sound measurements and mine was the quietest)