You know, I figured that and would have went that route had I thought it through completely, but originally I bought the 2 bros on sale, then after I decided I wanted a stainless header and that's how I ended up with the combo. The FMF header just seemed like the nicest SS header for the money. the butt dyno has noticed decent gains so far. Front wheel actually lifts a little in 1st on the power now that I have the fueling sorted, no way it would do that before. It's a hoot to ride now, probably mostly cause its loud as hell. From what I've read, I'm betting FMF can would get me another .5 hp, gains for full exhaust, airbox mod/uni filter, KLX needle and proper jet seem to be only around 3-5hp anyway, of course when you are starting at 31hp I guess that's pretty good. Bigger gains would be a 685 kit, ported heads and bigger valves, but hey, it's a KLR, let's not get out of hand. if I ever have to crack the cases I'll probably put a 685 piston in it, otherwise it's done as far as I'm concerned. I guess what I meant to say is, yes, you're probably right, that odd 4 stroke expansion chamber is probably tuned specifically for their cans.