2 stroke expansion chamber query

I installed a technigas exhaust on my Vespa a while back. It never felt right. There was never that "on the pipe" surge that should have been there. I attributed this to the fact that the pipe was intended for a 50-65cc bike and mine is 80cc.

So today I removed it to start fitting a YZ80 pipe and when I put it in the solvent tank to rinse it out I noticed that if I tried to drain it out the inlet side it held a lot of fluid.

So I did what anyone would do and cut it open to take a look inside. What I found puzzles me.

The header pipe extends into the chamber five and a half inches.

So what say you? Is that an intentional detuning restriction? Crap construction? or something clever that I am unfamiliar with?

That is quite a bit of extra material to include for free, so I can't imagine it is unintentional. It is supposed to be a high performance part so detuning it seems unlikely although it is a european market moped part so there might be some regulations pertaining to it that I don't know about.

Tempted to whack it off, smooth it out into a nice funnel and weld it back up to see what changes.

I haven't played with tuned pipes in a long time, and don't have my book handy, but my guess is they are trying to widen the power band and make it less peaky. Setup like that it will give you some power boost, but over a wider RPM range. Cut it off and weld it back, your power levels should go up, but it might end up being like a light switch, on or off.

You want to be really cool, make it sliding, and tie it into the throttle. With a variable length pipe, the power band is super wide. The exhaust pulses travel at about 1700 FPS. With a little math, you can figure how long you need to be at a given RPM.

The header-inside-pipe design will cause flow separation right as it enters the chamber. This will get rid of any "pipey" feel at all.

You might not do too badly to cut it off right where it enters the chamber and weld it on.

Or get the best compromise, drill it full of holes.

Cut it off and be prepped to do some jetting to get it right.

There are some generic 2 stroke programs where to enter in bore stoke port timing and exhaust port shape and rpm range and they'll crap out a pipe lay out. I'd do that then see how close your pipe is.