Hey I got a good one... you want Sexy Crome and sound...!
Got to a Moterbike Pannel Beater and grab your self the best looking or Biggest Moto muffler they have, The ones from Harley's and other thumpers I find to be the best.
Hey even get two and get another bit of header made or take to what you have with ya grinder...
These Mufflers have go over you existing piping and then tighten up with a nut and your away...
Make sure you have baffles inside the one you get and also ask how big the Bike it would have come off, A good yard stick is to go for one off a bike with 1/2 to 3/4 the cc of your engine, Keep in mind Bikes rev there titties off so you dub or sube will not push as much through it..
And MAN THEY SOUND HOT...
Exsperiment, Have a look at my playing around,
http://img.photobucket.com/albums/v365/Croppycam/Beach%20Buggy/BuggyRear1.jpg
http://img.photobucket.com/albums/v365/Croppycam/Beach%20Buggy/BuggyRear1.jpg