I'm trying to figure the compression on the LS1 I'm building right now. I found the stock LS1 has Piston Deck Height in Operation: 0.203mm / 0.008"
(Above Deck Surface) so would I enter that number in the deck clearance box as -.008?

My engine has Wiseco +3.2cc flat top pistons with bore size of 3.905, the 243 heads are milled to 60cc I'm shooting for 11.1cr, I'm trying to decide on getting Cometic .040 mls, Cometic .045 mls or GM .054 mls head gaskets.

Depending on how I enter the deck clearance either positive to negative there is about .4 difference in the CR.

 

Most calculator enter piston out of the hole as negative. You say flattop pistons but then list a 3.2cc dome piston. Which is it? If you really have +3.2, then CR is going to be something like 11.8 with GM gaskets.

 

The piston are flat top with 2 valve reliefs, the valve relief are added cc so they get added as +3.2 and dome would be -3.2 because it takes away cc.

 

Not with the calculator I use. Valve reliefs use a negative number because they decrease volume. In that case, use the Cometic .045" gaskets for 11 CR.

http://www.csgnetwork.com/compcalc.html

 

valve reliefs will increase clearance volume in all cases. The piston manufacturer will take that into account when specifying the net volume (+/-) that the piston contributes to the equation.

 

piston "out of the hole" is calculated with a negative value for deck height because the piston is reducing the clearance volume at TDC. However, I always thought the OEM deck height was positive (in the hole). What is your source for 0.008" out of the hole?

 

Stock LS1 pistons are usually around .006/.007 out of hole.