If you have a megaphone, a good example/test is to put the mega along different parts of the down pipe, so start off at the end of the pipe and then try it further along. I’ve found it works best if the pipe is several inches behind where it enters compared to just being in enough to be secure.
i knew i'd seen that somewhere. gordon jennings:
These several difficulties should convince anyone that a different approach to the
problem of effectively silencing the expansion chamber is required. Lacking a more
effective solution to the problem, we may eventually be forced to revert to a
straightforward muffler in place of the expansion chamber and live with the loss of power
and performance that entails. I do not believe that will be necessary, as I stumbled upon
a phenomenon a few years ago that meant very little at the time but now assumes major
importance: The then-existing general racing regulations required that a motorcycle's
exhaust system terminate at some point forward of the rearmost edge of the back tire, and
I was planning to race a bike with its cylinders reversed to provide rear-facing exhaust
ports (for reasons that were important, but not pertinent here). The only major flaw in
this scheme was that even with the motorcycle built on a longish wheelbase and with its
engine located well forward, there was not quite enough room for the exhaust pipes
within the length allowed by the rules. The expansion chambers themselves would fit,
but there was some 12-inches of outlet pipe left hanging back behind the rear tire, and not
enough room to curl these outlet pipes back within the limit. While groping for a
solution, I hit upon the idea of simply sliding them forward, inside the baffle cones.
There, they would still function as pressure-bleed resisters, and further contemplation led
me to the conclusion that the expansion chambers might even work better with their
outlet pipes positioned inside. With the forward end of the outlet pipe located at the
chamber's maximum diameter, ahead of the baffle-cone, there should be a somewhat
Two Stroke TUNER’S HANDBOOK
70
stronger reflection from the baffle, and that might very well give the engine a somewhat
better boost. Or so I thought.
Anyway, I gave the scheme a try, and while certain other modifications prevented
drawing any absolute conclusions from the experiment, the bike did prove to be very fast,
and it seemed certain that while my “inside stingers” might not offer any real power
advantage, they probably were at least as effective as those attached in the more
conventional manner. But that is not to say that I did not notice a difference - and the
difference was in sound. With those inside outlet pipes, the typical expansion chamber
crackle was very noticeably subdued. That made sense, as the chambers' outlet to
atmosphere was taken from a point where the pulse was at its lowest amplitude - rather
than from the high-pressure area at the tip of the baffle-cone.
^^^this is out of goron jennings two stoke tuner's handbook, a very exceelent read that covers a lot more than just two strokes. his chapter on exhaust systems is one of th ebetter parts of the book. available online in free pdf