The other major

contributor is the sonic waves in the exhaust caused by the rapid opening of the
peripheral exhaust ports.

This may make some cringe, but here goes: what if a small amount of 'ramp' were put in the wall just ahead of the port to allow some gas to begin exiting, or an inverted V notch. Not enough to make a noticable change in the exaust timing but just enough to take some of the "pop'" out of the pressure wave? This may be a subtle acousticle thing. Some people can really hear the difference between vinyl and CD's. The change of state as the port opens up is rather abrupt. What about pipe length to collectors tuned not to augment but to cancel? This may be all pooey... I know nothing in this area.
...Chrissi

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