3" pipe straight back and mandrel 90* out the side. Pics in the last post on previous page of this thread. Sounds quiet, but I'm coming from broken off right at the downpipe. Truck had straight through exhaust with a few bends out at 45* at rear bumper when I got it, cut that short when I put a 38 gal rear tank and exhaust didn't fit, then broke off, now out the side. No muffler on this truck ever and loudness has varied from slightly loud and droney with nothing but a downpipe, damn quiet out the rear and pretty quiet out the side. Turbo is a great muffler.
As for power, this thing has been a torqueless wonder since I got it. I wouldn't be surprised if my bike makes more torque. It is what it is and will do what you ask so long as you're patient. Nothing you do to the exhaust will make an appreciable difference. If you're never set the timing, do that. That made a night and day difference in both power and MPG (from 8.5 to 12 MPG) going from 6.5* to a about 9*, but it's still slow. Aside from that, cram more air and fuel in there and watch the pyro. Add head studs. Coming from a big block guy, I don't think there's much you can do to get more power out of these for cheap like on a 460. Head porting, better exhaust pre-turbo, but benefits are less than on a NA gas engine is my understanding.