As for the Ztec's, I really liked the way that ZtecRacing (Joe) has his setup. Let me find the link where he explains it a little.... [waiting on EDIT by mister slowpoke!

]
... Ok! Mr. Slowpoke is back and here is the link...
What Causes Rasp?
Basically, he has a dual exahust (dual tips) on his Ztec. He cut out the resonator and put a Dynomax Ultra-Flow muffler in place of it.