As soon as I find a donor stock can and can fab up my own $36 muffler, I will be installing a "quiet valve". Basically just a spring loaded flap that will be located about halfway down the can, which should open up at about 6,000rpms... SO, when the bike is running slow (under 5,000rpms), the flap should be fully closed and very quiet, and above 6,000, it should be as good as a straight pipe.... Unfortunately I don't have the exhaust can yet (ebay hasn't offered one cheap enough yet), so I can't do a write up on how I wanted to do it. This way, I won't have to worry about it being open or closed, just about where I want to run. Depending on spring weight, you could make it open later or sooner. I also haven't sat down to calculate what a good starting weight might be, so I can't even give you that... Sorry Felix. Hope this gives you an idea though.