I have an lq9 engine with 4.030 bore and 4.00 stroke, compressed thikness .030, the piston sticks out of the hole .010, have 67cc heads, whats the CR on the engine? Do you think we could shave them to 63cc without going higher than 11.5:1? I think I have around 10.9 but what do you say? Thanks

 

According the limited information provided and the assumptions below you are at approximately 11.89:1 now. If you go to a 63cc head with the same assumptions it will bring it up to 12.01:1.

Assumptions:
4.060 gasket bore
8cc valve reliefs in pistons
6.125 connecting rod

Calculation:

 

Forgot to say I have -8cc dish pistons, I gave it a try with the demo version of your software and calculated 11.56, it varies very little from the registered version cuz I cant get in some values but it sticks to it really good, thanks a lot pal

 

Are you planning n running this on pump gas? Because I am looking at the same motor, with 62cc heads.

 

Yeah this is running on pump gas but with 62cc I wouldn't use gas only. I would rather use alcohol or gas/vp, the problem here is the pistons are .010 out of the hole but if you use 0 deck height at tdc and .056 head gaskets your CR should be around 11.23 and gas only would just do fine.

 

How hard would it be to tune to keep it free of ping. How would a 11.1 or 11.5.1 motor like n2o?

 

calculation updated based on provided valve relief size.