Re: sbp expansion chamber?
I have a PK80 slant. There was a world of difference in power with a pipe. A big difference without "Tuning" (adjusting the length) right out of the box. As far as noise, the SBP pipe is pretty quiet during normal operation, if ya crank on it and it "comes on the pipe" I don't think it's much louder than stock, noise is coming from behind you(in my case).
Hope that helped.