I bought an engine kit from Summit with 9.3 cr pistons, took all the parts to the machine shop to be bored and balanced. They said the block deck and heads were a little "wavy" so they ground the deck and heads " just enough to clean them up for a good gasket seal" About how much would that effect the compression ratio?

 

It depends how much they cut off, and which head gasket you use.

 

The question was "About how much would that effect the compression ratio?" (meaning machine work) I have no way to know how much they took off. Just asking for an educated guess or average on how much effect the machine work would have on the compression ratio.

 

maybe .2 of a cr...
it's a total guess, why can't you ask the machine shop how much they took off?

if you have a caliper you can do some more accurate checks of your compression ratio as you build the motor.

 

For all we know they could have taken .0001 or .1 off. If you want to know what your CR is going to be youll have to cc your heads and measure your deck height and throw it all into a CR calculator.

But you probably are now running 9.5-9.7

 

It would help if you told us what size engine this is, and what heads they are. Nobody is going to be able to tell you exactly; but it might be possible to "bracket" it somewhat, to a range that it will fall somewhere within.

 

I guess i should have noticed that too.

They could be 9.3:1 pistons with 76cc heads and if your running 64cc heads your up near the 11s

 

I have a 355 with 64cc vortec heads. My motor has been together and running for a about a year and a half. Don't really care about the exact comprssion ratio. Don't have a problem, just courious about how much effect this would have. When someone asks what compression ratio I have I just say "about 9 and a half" I am looking for an "average" or "ballpark" or "probably about" answer.

 

My calculator says:

with 6cc dish, 64cc chamber, .025 deck clearance (stock), .039" head gasket; 9.7:1

and,
with everything else the same except .015" deck clearance and 62cc chamber (about .010"off the block and .015" off the heads); a little under 10.2:1

So, real world, you're probably somewhere in the 9.7, 9.8 kind of range.

 

sofakingdom, thanks for the info. Even though I now have a Corvette, I still have to come back to TGO for answers. (Unless I want to know if I should change my oil every 500 miles because "nothing is too good for my baby")
(This last remark is poking a little fun at another forum)