Where's the restriction? I have been comparing the stock muffler (insert removed) with the FMF power core 4 with "quiet insert". Don't laugh but when I blew through the stock insert, muffler off the bike, I actually felt some resistance. My friend laughed that there is no way I would feel anyting but to our surprise there was resistance but no black lips. I want a quiet bike for trails. The 450 has plenty of power no matter which pipe I use, but I was thinking the FMF let the engine run better. However, that quiet insert is anything but quiet. Their muffler is light with only a square tube inside. I think it was psychological that I preferred the FMF because I could not hear all the chinsy engine sounds you hear with the stock. But with resistance just blowing into the stock muffler means that there is significant resistance on the low end too? I like to ride below 1/2 throttle and mostly end up >1/4 when fooling around so low end power is paramount for me. I am worse than an old lady deciding where to put furniture on this one. Can't decide which muffler is better. Will the new stock replacement insert from Promotobillet be significantly better in spite of the muffler's internal resistance? Any other thoughts?