My fmf without a quiet core was about as loud as my coworkers harley with drag pipes when I got on the throttle.
The quiet core insert helped a little but it was still much louder then stock. On my 09 (with newer style carb) it went lean and started popping loud on every deceleration.
I had the opposite results of mrbracket. My fmf lost 4-6mph on the top end. After a year of screwing with the carb without any positive effects I sold the fmf.
My usual rides are 0 to 3000'
Remember the 03 and up TW's have a slightly different exhaust mount than the 87-02 TW's. It's off by about 3/4 inch.
Dustyg posted awhile back
"Most of the exhaust mods are the TW specific FMF powercore 4 and the TW specific DG round or oval series for the TW. The FMF Turbine 2 is not TW specific, but some have used it. To date, I do not believe anyone sells a complete aftermarket exhuast for the TW. It also depends on the year of your TW. See the info below for fitment.
The 2007 XT225 is the last year with a stainless header. The OEM part number is the same for the TTR and XT225. It will bolt up to the TW but is a little longer at the section where it attaches to the muffler. It can be purchased new at boats.net or stadium yamaha.
So, to recap:
1. OEM header and TW specific FMF muffler=bolt on. (2003 and beyond)
2. OEM header and TW specific DG muffler=bolt on. (2003 and beyond)
3. TTR 225 stainless header and FMF muffler=bolt on (2003 and beyond)
4. TTR 225 stainless header and DG muffler= cut the header (or add spacers to front and rear) and then bolt on. (2003 and beyond)
5. 2002 and prior bikes: The 2002 and prior bikes have a slightly shorter mounting tab on the frame and a slightly shorter distance between the two mounting points on the muffler. A short spacer is needed to link a 2002 or older OEM header to a FMF or DG muffler made for the TW "all years".
OEM muffler part numbers: