Whats up guys, it has been a while since I initially posted asking about a 09 KLX250SF. I love the bike as is, but it is a toy and toys always need extras right? That being said, I am planning on getting the Leo Vince X3, should I get a replacement header or keep the stock?

 

keep the stock, Put the header money towards a big bore down the road.
Dan

 

The stock head pipe is too small for performance. 1.5"/40 mm is the way to go.

 

If you dont want to buy a new aftermarket header, the klx300 stock header fits. Atleast thats what i've heard. Its bigger than the stock klx250s header

 

Thanks for the replies.
What is the difference in just having a slip on vs. adding the header also?
Is it really noticeable?

 

This is a good question. Some claim a big difference. Some have even said a header can reduce power. Others aren't so sure. I'm in the latter camp. We'd be well served to have some dyno test before/after, or at least do some well documented acceleration tests. I tend to agree with Dan above. If you want more power and are thinking of spending $300 or more on a header, keep on saving and get a big bore. If you can find a used KLX300 or other header for a good price, why not?

 

KLX300 header is the same diameter IIRC, so there wouldn't be a performance gain.

I would think the header would definately help, but i would put money toward a big bore above everything else and then add exhaust last.

 

Your memory is probably better. Thought I'd seen diameter numbers before, but couldn't find them. The same 18088 part number is used for the following bikes (Carl's Cycle microfiche)
2006+ KLX250
2005+ KLX300 (2004 is different number)
2008-09 KLX450.

That's right, even the 450! Can our header really be that restrictive when it's also used on a motor with nearly 2x the displacement?

 

Thanks Guys,
IDRIDR the info you provided really puts it into perspective for me. If the same headers are on the 450 as the 250 then it doesn't seem to me like they need to be replaced. I also read on another forum, Bill Blue did a dyno test with stock headers and with aftermarket while testing his 350 big bore kit. with the aftermarket header he lost 1/10.

This brings up another question and I didn't seem to find it anywhere. 331 VS. 350 VS. what ever else is out there I have not found. What big bore do you guys like and feel is proven reliable?

 

I ran my bike with the q4 silencer for along time cause my mega bomb was on backorder. I noticed a difference in snappiness and seemed to have more on top end. Was it worth the extra money for that slight increase? Probably not but its one of the most common areas to upgrade. Most run the FMF full systems. Im glad I did. Next would be big bore for me. The most popular big bore is the 351 kit. Everyone LOVES it!