Hi guys -- just an idea I got. I was thinking of making my own cannister muffler after looking at some of the threads on the subject. I was thinking of making the tuned type and setting it for a 23-8 prop or so. It then occured to me that perhaps there might be a way to have a servo-activated section of the can that would shorten or lengthen it. Then, you could mix this into your throttle -- sort of like a helicopter mix -- shortening the length for low rpms and lengthening it for high rpms -- thereby always being "on the pipe". My mechanic brother turned me on to this idea suggesting that I take a look at some car mufflers called Super Trap which have a same sort of thing he says.

What do you guys think? Stupid? Not enough benefit possible? Probably it would be pretty difficult to set up at first.

It can be done, and has been done. Something like the electronically adjusted camshafts for automotive 4-strokes that have broadened the torque range down to very low rpm.
The problem is in the seals, that need a fair amount of force.