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300cc kit in a 250cc xc-w?

8 replies to this topic
  • KTMrideR146

Posted June 22, 2009 - 08:02 AM


after this race season i am gonna replace the top end and while i am at it i am considering puttin a 300 kit into my 2006 ktm 250 xc-w (2 stroke)

just wondering how much something like this would cost and wat brands are the best.

  • OrangeYZ

Posted June 22, 2009 - 09:09 AM


KTM makes a pretty good 250-to-300 kit. They call it "300 parts on a 250".
I hear you can simply swap the 300 cylinder and piston over, but if the stroke is different, I think that would mess with either the compression or port timing, or both and you would need to change the crank too. No personal experience though.

  • mikes300

Posted June 22, 2009 - 10:10 AM


ya you can just bolt up the stock 300 parts, you need the cylinder, head, piston, and some power valve parts, gaskets etc, I believe KTM has just added a kit ( I think it comes with a black box too, but its not really necessary) to the hard parts catalogue, one is enduro one is SX, I think the head it the only difference.


  • trailmeisterjoe

Posted June 22, 2009 - 09:49 PM


One of the dirt mags just commented about one that they rode in a custom offroad bike test and said it was the best 300 they ever rode. different stroke made it a better 300...


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  • ac717

Posted June 23, 2009 - 05:28 PM


I think it was a 250sx with a 300 top end-converted to offroad. I also plan on putting the 300 cylinder on my 07 250sx. I was riding my crf450 and miss the bottom end pull. The torque and overall power is nice with a 300. My goal is going to be a broad powerband-with traction in mind. I am going to sell my beloved 08 200xc. I got on it today and after ridiing the 450 and the 250-I simply can't ride the 200 to its full potential. Guess I am getting old.

  • Iluv2fly

Posted June 23, 2009 - 09:51 PM


I just converted my 07 250xcw over to a 300 and it cost 1100.00 by the time I was done and that was with me doing all the labor. I would have been better off to sell my 250 and just buy a 300. I did use all KTM OEM parts.

  • Ttoks

Posted June 24, 2009 - 02:01 AM


the KTM 250 and 300 use the same 72mm stroke, the 300 is simply a big bore kit.

  • mikes300

Posted June 28, 2009 - 08:44 PM


One of the dirt mags just commented about one that they rode in a custom offroad bike test and said it was the best 300 they ever rode. different stroke made it a better 300...


the 250 and 300 share the same stroke, have since 2004


  • PSD_Sun

Posted June 29, 2009 - 10:14 AM


I have a 300cc 250SX. Also porting and head work from Munn and Dick's carb mods. I love that bike. Smooth awesome power from the bottom till it hits the rev limiter. Still not 450 fast but quite close I'd say.

I also rode the 2009 250XC w/ the 300 cylinder that won the Dirt Rider shootout as that is my local dealer and I'm friends w/ those guys. It definitely didn't have the pep of mine but of course it was set up for Hare Scramble and so it had the auto-clutch and some other stuff that made it less responsive than mine. Very nice bike however.


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