Setting deck height for 9:1 compression Options

[Chad911sc]

I have my short block built and I’m ready to set my deck height. It’s 96mm bore with stock 71mm factory crank. This is a 2.0 2056 build. I have a Web 86a cam calling for approx 9:1 compression. I have 60cc heads with 3cc valve reliefs on my flat top pistons. If I plug all this into the calculator, I get 8.3:1 for my compression ratio if I set the deck height to .040 inch
After I set up the piston on the rod and bolt down the cylinder to the block, I get .053 inch from the piston to the top of the cylinder.
My question is, what is the best way to proceed to get the 9:1 ratio with at least .040 inch total deck height.
I am thinking that if I take off 6 total cc’s from the head, that will leave me with 54cc heads with the 3cc valve pocket = total 57cc’s. Bringing me now to the correct 9:1 compression ratio with the .040 inch deck height.

If I am in the right ballpark, this means I need to have my heads fly cut….correct??
If this is correct, how do I go about calculating how many thousands of an inch do I need to have removed by the machine shop to remove 6cc from the head?

I obviously will need to remove at least .013 inch total deck height get to my .040 goal, and that’s with no shims or head gaskets being used.

Thanks for your time, Chad

[Jack Standz]

This should work fine for a shade tree mechanic rebuild, but for the little extra $$ (say $150), don't you want to have a machinist clean up the decks?

You want them flat (the glass and abrasive probably can get you there). You want them parallel to the crank centerline. You want the decks on both case halfs the same distance from the crank centerline.

As a bonus, the material removed will decrease your deck height and increase your compression ratio, which is what you said you are looking for. (If the cleanup cuts ends up farther than you want for your calculated CR, you can add the right sized spacers to dial-in the CR.

It looks like you've already glued the case half together, but just suggesting you might be happier knowing the motor is as good as you can make it. That's a sunk cost and it's still easy enough to pull apart and send to a good machinist.

The combustion chambers will also likely seal up better and longer if the parts are machined as good as you can get them.