Re: Expansion Chamber Questions
eDJ is abslutely right!
Just because a pipe looks better than the stocker does not mean it is offering a correct solution. Off the cuff I would have to say that just about anything is better, (pocket bike pipes etc.), than the stock pipe as far as performance is concerned, but ideally the pipe must be tuned to the engine.
I remember an article by "POPS" Yoshimura back in the 70's in one of the bike rags.
The short story: The volume of the expansion chamber is directly proportional to the amount of air the engine will flow. The shape is not that critical. Obvious by the fact that different motorcycle manufacturers had to tuck them in, in a variety of ways to satisfy the overall bike design.
The distance from the cylinder to the expansion chamber is dictated by port timing. When creating a tuned pipe for a new engne it is important to leave the chamber adjustable, (able to side on the header tube). By altering this distance you will get performance levels at different RPM ranges.
We would modify our MX'ers and then have to cut the expansion chambers off and retune them to go along wth the port work.