I have a 406sbc with flat top pistons. The pistons have two reliefs in them. Deck height of .020 and the combustion chamber is 66-67cc. I just bought felpro head gaskets with a thickness of 51, but now I'm wondering if I should have went with the 41 thick gasket. Can anyone please tell me what my c.r. is and which gasket I should use??? Thanks again

 

My calculator came out with 10.69:1 with the 51 gaskets. Don't know if it's exactly right since I guessed on a couple fields that were missing.

Somebody else could probably come closer.

 

If you want to get closer, you'll need to measure the top ring depth, volume of the reliefs, and valve face volume.

If you want a cheap-and-dirty calculator, you can load up this one: Engine Calculator.xls . I have it in QuattroPro format as well, and it has some enhancements in that mode (MicroSoft crap sucks, but it's cheap). Just plug in your numbers and calculate.

 

Thanks guys I just quickly cc'd my heads and they are more like 66-67cc.

 

I calculated 10.69 using a -5.3 cc piston crevice volume.

Your quench height will be out of wack with the .041 and the .051 head gasket. Use something like a .026 or .029 compressed thickness, and you will get 11 compression.

 

If the comp is 11 then I would not be able to use pump gas, right? What would happen if I ran the thickest gasket and the quench was out of wack? Thanks again for all the info everyone!

 

Are you using carb or EFI?

I think 10.5 is the limit on carbed cars, and the sky's the limit with EFI. I run 10.94 with pump gas 93 octane with no problems.

 

Its TPI and wanted to run pump gas thanks

 

Carb/EFI has nothing to do with compression ratio. What does is the camshaft and heads. Pick the right cam you might just get away with 11:1. Aluminum heads are more tolerant to higher compression ratios than iron heads.