Yep, preferably one very big silencer and, important bit, the right size exhaust tube.
Ours doesn't sound raspy.

350Z case in point - silencers too small, tube too big:

http://www.youtube.com/watch?v=JRmmu...eature=related

Single 3" exhaust tube, with one large (9" round, 16" long) silencer:

http://smg.photobucket.com/albums/v8...nt=buggy-2.flv


The same holds for the rotary, it just needs more attention as the note is naturally raspier to start with, so you need to go further to get rid.