There are many important things to consider when choosing a silencer for a KLR:
- sound.....the LV X3 and the Lexx with the quiet core are the two quietest that I'm aware of at 94db
- USFS compliance and spark arrestor; in the US or Canada you need a USFS approved spark arrestor to ride in most places - and even if you didn't you should have one to help avoid forest fires.
- weight - usually varies from 5 lbs to 8 lbs vs 11lbs for the stocker. FMF Q4 weighs 5.7 lbs, my LV X3 wieghs 7.7 lbs.
- maintenance - all packing type silencers will require periodic repacking; the only silencers that don't are the LeoVince X3 and the Staintune from Australia.....I don't recommend the Staintune for a variety of reasons but the cost alone is prohibitive for most.
- power; there is a small amount of power to be had with the corresponding jetting and airbox changes but don't expect miracles and most of the "butt dyno" reports are due to noise rather than power. ....you're looking at a 2-3 hp at best.
Of the two you mention; the FMF powercore is too loud, the FMF Q4 is 96db and is on the loud side of acceptable (both for the general public as well as most ORV parks which have a 96db limit). The FMF is an easier install, is very light and has the USFS spark arrestor. The Lexx is cheap, relatively quiet and of the two would be my choice. I have a Q4 on one KLR and a LV X3 on the other.......I far prefer the X3 despite the extra 2 lbs.