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2011 YZ250 CYLINDER head

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I just bought a low hour 2011 YZ250. I found that there were a few changes that year to align with Europe models. One was slightly less compression ration. I found only the cylinder head is different than earlier years. I still have my 2009, and was thinking of swapping cylinder heads before I get rid or it. I have been riding yz250's for years now and have my fuel (50/50 w/ 110 octane) and jetting figured out and am not worried about top end failures at all. What do you y'all think, worth doing?

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Ive found its better to leave the old with the old. Send to Pro Circuit for mlling and squish checking and hell, have it replated while you're n it. Throw in a new piston and roll. Besides, the difference in compression is only for the fact that Europe doesnt have mandated ethanol and a couple of RON points better octane. US and most North American fuel is standrd 10% ethanol, thus our need for lower compression and octane, despite what the manual tells us.

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I would measure the Squish and Volume on both and then decide what to do?

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I say do it for now since you have both right now. you will get the increased compression you're wanting (somewhere around 10.9 to 1) since the 09' head has less volume than the 11' but I would send it to RB designs the first chance I got to have the head modified.  Do the squish test on their website and send them your head and request they don't mess with the dome (unless you're wanting to keep your compression around 10.9 to 1).  This will raise your compression even more but will require race fuel for as long as you're running that head... :thumbsup:

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I say do it for now since you have both right now. you will get the increased compression you're wanting (somewhere around 10.9 to 1) since the 09' head has less volume than the 11' but I would send it to RB designs the first chance I got to have the head modified. Do the squish test on their website and send them your head and request they don't mess with the dome (unless you're wanting to keep your compression around 10.9 to 1). This will raise your compression even more but will require race fuel for as long as you're running that head... :thumbsup:

:rolleyes:

Edited by Monk

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I would dump your 50/50 mix and just get a good quality 94 octane...

I would set the squish and depending on elevation, I would make my decision on the dome. The difference between your 09 head vs 11 won't be noticeable. There is no need to increase compression...

Edited by Monk
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Running more compression means nothing...

And the OP never mentioned anything about bumping compression either...he just has two heads with neither being cut...

Edited by Monk

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