In the interests of science, here's the next layer in the stock European-issue KTM640 SM exhaust. With a lot of crude drilling and cutting. I removed that mysterious plate shown on page 1 of this thread. This pic is what I got - the next layer. This next plate (the one shown here) is about 2 or 3 inches deep into the back of the muffler - probably at the same place that the US exhaust would have the bolts for the Supertrapp discs? Maybe this Euro-muffler is simply designed to be not modifiable. The sound of the exhaust has changed very little. Up a decibel or 2, a bit less mushy. Performance, dunno yet. Haven't done anything yet to jetting or airbox. Maybe I should just leave well enough alone and save my pennies till i can get a Staintune or the like.. Comments?