I've done quite a bit of research on this and have tried a few different silencers. I currently have a Q4 on one KLR and a LeoVince X3 on the other. Thoughts;
- 1) use a gen 2 header; it's mostly just looks but it stays looking decent compared to the clamshell welded gen 1 unit. I don't believe the powerbomb or any other header pipe gives you a noticeable power boost.
- 2) Several of the big name pipes are too loud (2 bros, Yosh, etc.) I try to stay under 96db (and our trail system polices this)
- 3) There are several things to consider
- sound; lower the better
- spark arrestor
- USFS compliance
- maintenance (most need repacking.....only ones that don't AFAIK
are the stock one, the LeoVince X3 and the Staintune)
sooo....the Staintune is said to be a good quality unit but it is ridiculously expensive (and this coming from someone who has spent over $3k in mods on each KLR), and I couldn't get answers to some of my questions regarding fitment, weight and noise level.
The FMF Q4 is .....acceptable as far as noise, relatively inexpensive, fits perfectly, has USFS approved spark arrestor, its very light and is clearanced to miss the rear caliper when the rear suspension bottoms. Only downsides IMO; it isn't the quietest and will require periodic re-packing (the frequency of which is often overstated)
The LeoVince X3 is quieter than the Q4 by a couple decibels and doesn't require repacking....still has good tone (no more sounding like a briggs and stratton lawnmower engine). as a two pce design it is a bit more of a PITA to mount and install and it's also a couple lbs heavier than the Q4. Back to back drag racing suggests that the additional db reduction doesn't reduce power compared to the FMF.
I've also heard good things about the bargain basement LEXX unit though some replace the springs with better ones and the packing can also be improved. Like the LeoVince it comes with a variety of tips though IIRC you have to buy the enduro tip separately...which is the one you want.
Hope this helps,