I have a FMF Gnarly pipe and FMF short silencer on my 99 cr 250. It seems no louder than stock. It gives the bike more torque down low but takes away some of the top. Ive had good luck with FMF in the past. I wouldnt hesitate to go with FMF again.
I've been using FMF stuff on my bike, non probs w/their pipes or silencers on mine.. I did try their pipe springs, lost them within a few minutes, junk.. Other than that, no probs, bike makes HP everywhere..
I went from the shorty silencer to the TC2 sparky and lost a little of the low end snap. Being in Cali, I had to use the sparky. Sparky seemed a little quieter than the shorty, but not much. I have always had good luck with FMF stuff.
If low end boost is what your looking for the fmf factory fatty is the pipe you want and match it with there T2 silencer its the best combo I've ever had but you do loose alittle top end but love the bottom and it sounds awesome.
I just put a FMF SST and Shorty on my 04 YZ250 and I love it now. It doesn't seem to be much louder just seems like it is a lower pitched tone than the stock silencer. It took me all of about 30 min to install everything and this is the first pipe I have ever put on. I love this combo and would recommend it a little stronger off bottom way stronger in the mid and just about never stops revving. It will pull unexpected wheelies in 4th gear now!!