High Compression Piston requirements

7 replies to this topic
  • fastyz250

Posted December 13, 2011 - 05:04 PM


Hey guys, I got a really good deal on a cp 13.75:1 standard bore piston and was just making sure that i can run this with my stock cams? Im completely rebuilding the whole bike once the ground is frozen, new crank, all new bearings and seals, having the head ported and pretty much whatever the bike needs its gonna get it to a point. i know what fuel im planning on runnning so thats not a problem and im going to send out my cylinder and new piston to get the cylinder replated and matched to the piston. i just wanted to make sure that i dont have to have cams for this to work? im sure that if i do get cams then i would be unleashing the full potential of the piston. the bike is a 2006 yz450f with full factory 4.1 and megabomb exhaust, k&n filter (for now), boyesen qs3, jd jet kit, and im running engine ice with oversized rads. Thanks for looking.

  • geshields

Posted December 13, 2011 - 07:10 PM


You don't need new cams. I had a CP 13.5 piston in my 2007 YZ450F and it was a nice improvement in power. More torque on the bottom end...I could run the 13.5 piston on super unleaded without any issues.

  • fastyz250

Posted December 13, 2011 - 07:21 PM


OK cool thanks that's exactly what I wanted to hear is from someone who has one. Thanks

  • geshields

Posted December 13, 2011 - 07:29 PM


When I changed the piston out, I replaced the piston with the CP 13.5, cam chain with oem cam chain and valve springs with new oem springs. Valves were still dead on from new so I didn't swap those out.

You are going up one notch on compression above mine so your experience may be slightly different.

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  • fastyz250

Posted December 14, 2011 - 04:02 AM


Yeah I'm going to check all my valves and springs when I tear it down I already have new valve seals and ill definitely check all of the springs I'm probably going to get a high rev kit or something. Did you notice and change in reliability?

  • geshields

Posted December 14, 2011 - 08:12 AM


No change in reliability. I put it in at 80 hours and the bike probably has about 120 hours on it now. I sold it to a buddy of mine (at 105 hours) so I don't know the exact time on the bike now. He hasn't mentioned anything abnormal to me...

  • beezer

Posted December 14, 2011 - 10:49 AM


You don't need a high rev kit cause the bike will rev less with more compression.

I put that piston in my dirt track bike and it gives the bike more low end.

  • fastyz250

Posted December 14, 2011 - 01:19 PM


ok cool yeah that actually does make sense hopefully everything else will check out ok then when i pull it apart thanks for all of the feedback its really helpful one of my buddies has one in his dirt track bike and he says he loves it

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