I run an FMF Shorty on my 250. It has noticeable power improvement over stock silencer. I am sure that PC pipes are awesome for kx's. Alot of FMF fatty fans on other makes of bikes, but the fastest kx hillclimbers and most knowledgeable guys on here, all agree that PC pipes work the best. I am just not sold on their silencers. I use the FMF powercore ( no shortys for 500's) for the k5. I have ran the PC platinum with great results. I recently put a stock pipe back on it, (still have FMF silencer) because I found it for 35 bucks and it was brand new. I will be be buying new PC Platinum ASAP, because I lost alot of hit everywhere. Stock is great for trails, but lacks the thousandths, that I need. I cut a silencer in half last year, where it didn't stick past the number plate. VERY LOUD, but worked well. The only adverse affect to that may be running temps. I was warned that I may be flirting with temp problems, but I don't race endurance type racing, so was no issue at all.
On the 250, I ran PC pipe with stock silencer. Had to raise the needle to smooth out hard hit during mid. Ran way better, but improved even more with FMF shorty silencer add. I have to switch back to stock to ride with spark arrestor(doesn't fit the FMF) and can tell power difference.
My thoughts, which may be wrong, are that if it makes it louder, its probably making it faster.
If it makes it more quiet, you can ride it in more places.
Anyone have an opinion about how tight packing should be wound?
