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View Full Version : 250x to 300ex topend conversion


SET THE STAGE
03-20-2006, 05:15 PM
is there anyway to put a 300ex topend on a 250x to add more displacement/power? just wondering because i might get a 250x soon and figured that'd be an easy way for a little more power
TarheelRedRider
03-20-2006, 05:35 PM
yes its a direct bolt on but you will need to change the crank to get the displacment change. The stroke on the 300ex is what gives it the bigger displacement not the stock bore.
zeppelin
03-20-2006, 06:32 PM
^^^ this is true, but it would be a waste of time to try to replace the crank too because you'll need to machine the cases for it to fit.
SET THE STAGE
03-20-2006, 06:46 PM
ic, well are there any decent big bore kits for 250x's? or any for a 300ex that would fit it?

i plan to get a curtis sparks pipe right off the back as soon as i get it, and then get a 400ex front end setup until i get enough money for some 300ex arms
TarheelRedRider
03-20-2006, 07:10 PM
Depends on how much you want to spend, You can make it into a 396 like I did. Just alot of work and a nice chunck of change. If it runs good just ride it till you need to do the work. ;) Best advice I can give you.
2muchquad
03-20-2006, 07:13 PM
there are all kinds of kits out there,you can go with the 2mm over bore(.080) which is good for 398cc on the 300ex or 262cc? or so on the 250x.it really comes down to what your willing to spend:)
SET THE STAGE
03-20-2006, 07:21 PM
ic, thanks guys.

might i add this is also my first 4-stroke quad so i'll probably be asking questions a lot like with cams and stuff 'cause i don't know any of that stuff. i've always been a 2-stroke guy but all my quads got stolen and i found a super good deal on a 250x
TarheelRedRider
03-20-2006, 07:30 PM
Thats what were here for. Try using the search button first or alot of guys here will complain about having all the same questions asked over and over. I dont mind.
zeppelin
03-20-2006, 07:35 PM
Originally posted by TarheelRedRider
Thats what were here for. Try using the search button first or alot of guys here will complain about having all the same questions asked over and over. I dont mind.
i dont mind the technical questions like this one either. most of the time its when someone asks which pipe is best for my bike or which is better uni or K&N that gets people mad.
SET THE STAGE
03-20-2006, 07:52 PM
oh and tarheel rider, do you have any tutorial thing on your 450r rear end? i saw that and it really caught my eye.
Cody_300ex
03-20-2006, 08:03 PM
Check this thread out..... http://www.exriders.com/vbb/showthread.php?s=&threadid=195797&highlight=300ex+engine
SET THE STAGE
03-20-2006, 08:06 PM
thanks brahh
TarheelRedRider
03-21-2006, 07:29 AM
http://www.exriders.com/vbb/showthread.php?s=&threadid=207520 and then here http://www.exriders.com/vbb/showthread.php?s=&threadid=214054.
This should give you all the info on what I did and how and all the questions in between. Im still in the test stages of it and plan on having some prefab brackets made to sell so everyone that wants to do this can. Like to make it a simple bolt on mod.