Building a new ls3 and my pistons are out of the hole .006. I was planning on running .040 head gaskets but that only gives me .034 quench. Is that too tight? Should I just use .045 gaskets and be @ .039? Heads are milled .030 and the .040 HG would put me around 11.5-1 cr which is what I want it to be. Using the .045 puts me around 11.2-1.

 

The ideal quench is between 0.035 and 0.045 or so, so you're good. Lots of people go with 0.040 Cometics on the LS2s and LS3s which tend to have the pistons around 0.006-0.007 out of the hole.

 

So I'm safe at .034?

 

Yes,the aluminum block will grow about .005 so you are at .040"

 

That depends on rod material and rpm. I wouldn't go any tighter then .040.

 

You'll be fine. If you are running an aluminum rod you would want a tad more.
I ran a 496 BBC at .031 with shifts at 6500 rpm and never had contact. I pulled the heads at 20000 miles for a refresh and looked great. Pistons will stay cleaner.

 

I'd run it. I set mine at .036" with an iron block and stock bottom end. As mentioned by Ari, the aluminum will expand with heat and will increase the quench.

 

Quick question about quench.
When figuring quench with dished pistons. How do you measure that?

Example. Ly6 stock block. I think the stock pistons measure -6cc.

Sorry not trying to hijack, more like piggy back.

 

From the flat portion on the piston to the deck of the head,you use a dial indicator or a bridge for accurate measurement how far the pistons sticks out from the deck but FI wants to be set loose

Allso to consider with tight quench is piston rock and piston material Cast pistons run tight clerances so they rock less and then grow very little,some pistons have bad skirt desings to be run tight

Iron block with cast oem pistons dose not grow much,with Kents .036" quench is an accurate number less then waht you are running and he probably pics up good power by doing that