hi comp piston or shave head

I have a crf 80 which has been ported hot cams stage 1 flat slide and pipe it has to stay under 85cc class limit it runs standard piston I have been told to shave head others have said to go hi comp piston Second if hi comp piston whats available Thanks in advance ant

Shaving the head will give you the same result as a high compression piston if you go to the same compression ratio. There are more things you have to worry about if you shave the head though. You have to make sure you have enough valve-piston clearance for one. Depending on how much you shave off the head you will have to degree your cam (I believe your engine is overhead cam correct?) since shaving the head will throw the cam timing off a couple degrees.


A high compression piston made to fit your bike with proper clearances would be the easier route to go, though you should still double check all clearances to make sure they are good.

Ya I'd go with a high comp piston and use modeling clay or play dough  and check the PTV clearance.If you have a good bit of clearance at that point you could have the head milled to raise the compression a bit more.I wouldn't mill too much off thought since you would have a hotcams cam and high comp piston clearances are getting tight.As far as timing is the cam sprocket adjustable on that cam?

might question cost of oem piston vs high compression,  multiplied by how many you change in a race season.  Could be cheaper to cut the head or deck the cylinder, or peel a layer off a gasket , or run solid face valves, or....?

Edited by highmarker

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