2009 yz450 top end

7 replies to this topic
  • Yzflier977

Posted January 24, 2013 - 07:23 PM


Going to do a top end rebuild on a used 2009 yz450 and was looking at going back either stock or considering the CP high compression piston kit. I was wondering about the pro's and con's of the high compression? I know OEM is practically bullet proof and I've heard good things about CP products so I really could go either way here. Would I have to run race gas if I went high compression? Also does the high compression piston change the power delivery in any way? Is longevity an issue with the high compression? Any feedback is much appreciated. Thanks in advance.

  • Mark537

Posted January 24, 2013 - 08:37 PM


I have the same bike and had the same question a few weeks ago. Everyone told me to go with OEM. So that is what I did. I haven't installed it yet hopefully next weekend. I am interested to see what others have to say about the other questions you had as far as longevity and power delivery.

  • Yamaryder29

Posted January 25, 2013 - 04:38 AM


I just purchased a complete oem top end piston kit from ebay for a total of $145. It comes with everything needed to change your piston. I havent found anyone else that can come even close to this price. Here's the link.


  • Yzflier977

Posted January 25, 2013 - 08:08 AM


Jeez! Der29, thanks man. At that price I couldn't afford not to go back OEM. Thanks for the info.

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  • Yamaryder29

Posted January 25, 2013 - 04:48 PM


Jeez! Der29, thanks man. At that price I couldn't afford not to go back OEM. Thanks for the info.

I know what you mean. I had a friend trying to talk me into a high comp wiseco, but I can see spending the extra money when I'm not even using the stock power to its full potential.

  • hackman162

Posted January 28, 2013 - 08:12 AM


I'd still like to hear the pros/cons of the high compression (13.5:1) pistons. I can get a CP kit, with gaskets, much cheaper than the OEM quoted above. I also have a source for 100 octane race gas out of the pump, so I am willing to use that if it makes sense.

  • Yzflier977

Posted January 28, 2013 - 11:27 AM


Hack, I'd still like to know as well, but since none of the "experts" have chimed in with either an opinion or personal experience I decided to go ahead and go with the OEM this time. Maybe at some point I'll get answers to my questions. It'll be 100 hours or so until the next top end so I have a while to do my home work, lol. Thanks for all the input guys.

  • grayracer513

Posted January 28, 2013 - 11:55 AM


The probable reason that none of the "experts" have chimed in is because as odd as it may sound, you aren't the first one to have ever asked this question. In fact, it's been asked so many times before that any search of the forum for "compression" and "fuel" or "gas" would likely produce hundreds of hits.

Nevertheless, in most cases, higher octane fuels are not required. Near sea level in the summer could be an issue, or if your normal pump premium is garbage.

Increasing the compression ratio tends to improve power more in the lower range than at high RPM, but it does add power across the board. But is it worth the money over OEM? Is the trade off in longevity versus OEM worth the extra power and price? Neither one, IMO.

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