JDMC5

iTrader: (3)

I'm having a little trouble coming up with proper numbers using summits compression calculator. For example, when I plug in the stock numbers for either an LS1 or LS6:
LS1 LS6
Bore: 3.898 3.898
Stroke: 3.622 3.622
Head volume: 66.67 64.45
Dome volume: 0 0
Deck clearance: 0 0
Gasket thickness: .052 .052
Compression ratio 10.22 10.5

this is all fine and dandy, however when I measure my deck clearance I find my pistons are .006" out of the hole, giving me a compression ratio of 10.36:1. Did GM rate our engines assuming 0 deck clearance or what? What are your guys thoughts on this?

I'm doing a build using stock flat tops, .052 gasket, 243 heads. I plan on doing some mill work to my heads and possibly taking a few thou off the deck, I need to make sure my math is correct. I plan on running a stock head gasket which should give me a quench of .046" and a compression ratio of 10.65:1 before any machine work. I want to run closer to 11.0:1. Do I throw the factory ratings out the window and do my own math or start from the factory rating and work from there? I need your help.

LS1MCSS

iTrader: (18)

If you mill the heads .030 to get the CC down to around 62, that will put you at 11 to 1.

A.R. Shale Targa

iTrader: (2)

Approximately 0.0067"mill equals one cubic centimeter of volume...so a .030
cut would put a 243 casting at about 60 cc total volume.
Also to the OP...the Summit calculator assumes the gasket to be bore diameter which it's usually about .100 larger. GM probably figures about 1cc
of primary ring land volume (around the top of the piston to bore clearance)
as well as manufacturing tolerances.

JakeFusion

iTrader: (7)

The LS1 has a higher than 10.1 CR. It's around 10.3:1 everytime I calculate it, even with the larger gasket creating more combustion chamber volume.