10.5 to 1 compression ratio on a predator 212

[661_Minis]

Hello, I’m building a predator 212 non hemi and need advice on achieving a 10.5 to 1 compression ratio, how much should I shave the head? I haven’t measured how deep the piston is in the hole yet because I already took the whole engine apart and I’m waiting on my ring compressor and other parts too come.

HERE’S WHAT I ORDERED
3.308 rod
Billet flywheel
292 nr racing cam
26lbs springs
1.1 champ rockers
.18” mls head gasket
3 stage center exist header pipe
Chinese vm22 carb & manifold (with jet kit)

I will be ordering CM pushrods after I measure and see what size length I need. Also I am planning on porting the head, I just need more tips and advice. Give me your guy’s opinions on the build, if there’s anything I should do or change, also this engine will be going on a mini bike.Thanks

 

[ole4]

You need the in the hole measurement, and head CC's first. then you need to have a minimum of .030 clearance between the top of the piston and the flat squish area of the head which you get thru head gasket thickness. Once you have your in the hole, gasket thickness and head CC's you can use any of the many online CR calculators, then if the compression is not what you want you can plug in alternate values for CC's to see how many CC's you need to remove to get your 10.5 compression. Your list did not include a flat top piston which you would want to cheaply increase the compression ratio if the current piston is dished. There are two different compression heights on the flat top pistons, .550 and .570, Hemi piston being the shorter one.