What's my compression ratio?
 

I've got milled LS1 heads. The combustion chamber cc's out to 61cc (stock is 67cc). I have a stock shortblock (read stock pistons and stock head gasket thickness). Some of you compression gurus should know this. I think the compression height of a stock LS1 is .005" positive, but I could be mistaken.

Thanks,

Patrick

Re: What's my compression ratio?
 

According to GM, the stock compressed head gasket thickness is 1.33mm or 0.0523". If you use 4" diameter for head gasket hole, then the volume of the compressed open space between piston and head is roughly .657 cid or 10.77cc. Of course the LS1 piston actually sticks up above the block by about 0.007" stock, so you will need to subtract this 'piston above deck' volume. Using a 3.9" diameter piston and a negative piston deck height of 0.007", you get -.084cid or -1.37cc for the piston above deck volume. 10.77cc-1.37cc=9.40cc. But then you have to add back the volume around the top piston ring which is approx. 1.2 cc. So 9.4 + 1.2 = 10.6cc.

So with a 61cc combustion chamber:
61cc+10.6cc=71.6cc. (709cc+71.6cc)/71.6cc = 10.90

Re: What's my compression ratio?
 

Wow, what a fast and informative post John. Thanks! Everyone else concur?

Re: What's my compression ratio?
 

FYI:

Some stock LS1 dimensions per GM:
Stroke: 3.622"
rod length: 6.098"
block deck height: 9.240"
piston comp. height: 1.338"

piston to deck ht.= block deck ht. - [(stroke/2)+ rod lenght + piston comp. ht.]

9.240" - [(3.622"/2) + 6.098" + 1.338"] = -.007"

So the piston sticks up .007" above the block. The negative sign denotes the piston is above the block. Most conventional engines have the piston slightly below the block deck and would have positive piston to deck heights.

Re: What's my compression ratio?
 

Using the stock LS1 numbers like John, I get 10.89. So I guess that means John is correct. <img src="images/icons/wink.gif" border="0">

Eric