So I have a full-dual exhaust that runs two pipes all the way out with two mufflers, one at each end. (And an expansion chamber in the middle of each pipe.)
It's quiet enough to be under 92db at the track. (The quietest limit so far around here.) Plus, since the mufflers are at the ends and they only service one rotor apiece, they don't seem to die.
A lot of people run a single, 3" pipe setup with a muffler in the middle instead of an expansion chamber, and with another muffler at the end. These systems seem to be quite enough for 92db, I think, but they also eat mufflers from heat.
If you don't run a second muffler in the middle of the exhaust, you will probably run about 98-100 db from what I understand. But I would love to hear from someone who dyno'ed a single pipe exhaust with both mufflers in place. A single-muffler exhaust making 100db does me NO good since I can't race like that at my home tracks.