[MoTrFinger]

i dont know the full science behind it, but some back pressure is needed for 4 strokes, but not a lot.

stock exhaust are pretty restrictive and i personally hate the sound of them. with a full exhaust and pc3(r) you can usually get 10+hp with them. aftermarket exhaust's also usually shave off 10-15 lbs. (full arata exhaust on a 600RR is 10+ hp and -15lbs!!!)

I have a full titanium exhaust from Arata for my 04 Busa. It gives a few extra hp especially with the PCIIIr but when I put the new exhaust the handling of the bike improved dramatically. I shaved off closer to 40lbs with with mine (went from 2 canisters to 1) and took off some of the weight where it made a big difference (up front) especially under braking.