2 reasons, and I may wrong. But one of the guys was here doing testing and found the bomb lost 1/2 hp over the klx headpipe.

the other is the cam timing at 1mm lift on the stock cams has no real overlap that pipe tuning would really benefit. The way the cam timing is back pressure is the only real help or hurt. The bomb being an ANTI resonant device, is neither helping or hurting the exhaust system tuning on this motor. If there was a longer "lowboy" style head pipe it would help more. Tuning wise the stock headpipe is too short, but with the cam timing it really doesn't matter much.

 

i don't know about the stock displacement but i'm putting a full exhaust on my 331 -


from thread https://www.kawasakiforums.com/forum...lx351sf-29316/

 

I just finished those mods on my 2012. It's a world of difference from stock.

Instead of dropping $500+ on after market exhaust I bought a used exhaust system from 04 KLX300 on Ebay. This made a HUGE difference. Cost: $125.

I have an extra KLX300 header pipe for sale...

 

Those are some good numbers. Which 331 big bore kit did you install?

 

Noticeable??? The stock bike couldn't get out of its own way. Now... If I were a wheelie-type guy, I am sure I could do 1st and 2nd gear wheelies easily with pretty much just the clutch and throttle. It pulls *that* hard now!!! BTW - I am not sure the KDX snorkel has any real benefit to it. I may go back and try the stock one again, as some report better performance with it. I did go with a rather obscure exhaust system, which may account for much of the added power. <DEP Exhaust"/> A bit of a warning though... I *DID* have to do some mods to make it fit... cutting down the flanged end of the pipe and welding a short (4" or so) piece of pipe on the end. Looks wicked cool, and sounds fantastic too... along with gobs of power... it's a winner!

 

I'd get that if I was you. Has a larger diameter, although it's shorter and won't match up with the newer model aftermarket slip-ons. Then you'ld need to go with the klx300 slip on (stock or aftermarket)to match up. A used muff from a 300 would save $'s and you'ld still have a quieter exhaust (if that's what u want).

 

I have a cycle pro 331, basically the same as the Kustom Kraft but uses a rebored rather than brand new cylinder.

Those aren't my dyno's BTW, see the thread I linked to at the bottom of my post if you want more info.

The KLX300 header is the same diameter as the new model KLX's but is acutally LONGER than the new 250's. doubtful you would see performance gains other than just a better muffler if you went with a stock 300 exhaust IMO.

 

Yeah, what he said. Don't know what my brain was quoting.
I'm running the FMF q4 with stock header on an '09. when coupled with the air box and jetting mods it made a night and day difference . But then again, so did the big bore kit later.

 

That's good to hear. I was interested in the header pipe until I read the rest of the page...dang.


Now that's what I like to hear. Since I will be riding it on the street, I want it to have as much power as possible, but still be reliable. Know what I mean?

Thank you, very informative. The dyno graphs show huge promise. I'm def a dyno type of guy. I like to know before and after, as my hobbies include performance cars as well. However, a slight monkey wrench has been thrown into the plans. I read the thread on here about the 2013 Honda CRF250L that linked to other threads about it comparing the KLX and the CRF. Now I'm confused! It seems as if the CRF weighs more, but performs better, has newer technology and costs less. UGGGGGG, what to do! I already had all the performance mods on my watch list on ebay for the KLX!!

 

In what ways does the honda perform better than the kawi ?

I wouldn't be surprised if the suspension was better from the factory as kawi did cheap out pretty bad on the valving of the KLX.

Engine output will likely be about the same stock, as i think the honda uses the same motor as the CBR250 so probably about 20-22hp.

Again, not trashing on the honda, but just not seeing what all the excitement is about on that bike.