im rebuilding my 250x engine and want alittle more compression. i know the 300ex and the 250x have the same bore size. wiseco makes a piston for the 250x but its 12:1 which is alittle too much, but the 300ex piston is 11:1 so i was wondering if the pistons are interchangable?

 

The bore of the 250 and the 300 are the same, the 300 has a slightly longer stroke, giving it the extra cc's. I would assume the piston would be slightly different to allow for the longer stroke, but I am just guessing. Best thing would be to call a dealer to be sure.

 

yea i didnt think about the stroke being different and how they could have moved the piston pin and such. it just sucks cause around here the shops do not have pistons in stock to compaire the two.

 

what will 12:1 compresion do to your engine, i've had one for about a year and my starter is fine, but you wouldn't really have that problem.

 

i'd like to keep running pump gas...12:1 is alittle much for 93oct.

 

I'd double check on that, I ran a 10.25 piston in my Wolverine for years with 87 octane, no problems, i think 11.5-12 : 1 should be ok with 93 octane, any shop could tell you for sure, I believe a lot of the new sport 450s run 12:1 pistons from the factory, and run fine on 93 octane premium.

 

i emailed wiseco and they said it was a no go on pump gas for the 12:1. i ended up ordering a pro x piston kit. 10.25cr isnt really that high you can run pump gas but when you jump into the 12's and higher race fuel is a must. i think the newer quads can run high cr's cause the technology is way better now then it was back in the 80's lol. you look at my 250x head and combustion chamber campaired to a new 450....huge difference.