i am building an iron 5.7 with 243 heads with stock thickness head gaskets (.052 if im not mistaken) and the block will be square decked. i was going to use stock pistons but now i might buy some forged pistons with a -4cc dome.

1) what is the stock ls1 piston dome size, 0cc?

i want around 11.5:1 compression with the 243s. (64cc stock i believe)

2) how much do i need to mill the heads to reach my goal cr?

down the road i might decide to put a procharger or somesort of FI on it so i will probably switch to 317s (72cc stock i believe) to lower the cr.

3) with a set of unmilled 317s where will my cr be?

sorry, im just trying to figure all of this out but i guess im not smart enough to do it.

 

http://www.rbracing-rsr.com/compstaticcalc.html

This is the one I have used several times recommended by Predator-Z on ls1tech.

 

Honestly i don't think you can mill 243 enough to get you to 11.5:1... BTW stock ls1 is 10.0:1 with a ~66.76cc, and 243s are ~64.45... So with the stock piston your would have to mill the heads down to a 56-57cc, not wise IMO.... Then again, my numbers may be way off...

BTW what made you choose that particular number... Everything i have read on these motors is try and stay below 11.0:1 to run decent gas and timing...

 

i just wanted to get around 11.5:1 for the extra power since i already want to mill the heads. i have never read or heard about staying below 11.0:1 on these engines but i will definitely do that now.

i will try to figure out that calculator again, i tried earlier but i dont know the deck height to complete the equation.

 

Deck height on a stock ls1 block should be about 9.24 inches. Here is a good website with a bunch of ls1 info on it:

http://www.smokemup.com/tech/ls1.php

Good luck with the build. I am looking at doing the same combo in my truck with the exception of using 5.3 heads pp'd with larger intake valves and stock pistons to achieve the 11.# to 1 compression.

 

I also found this over on ls1 tech when I was doing my research. It is fairly accurate if the pistons are stock and the block is stock. The head gasket could be different but it only accounts for a tenth or so in compression from what I have read.

https://ls1tech.com/forums/advanced-...ume-vs-cr.html

 

i have read that too, milling .010" is about equivalant to taking 2cc's away from the combustion chamber, right?

EDIT: after reading the ls1tech link more closely it appears that .010" accounts for 2cc's in the combustion chamber. so if i am using pistons that have a -4cc dome and i mill the 243s .035" i should be close to 11.0:1 compression ratio

 

actually if you read more into that thread, it states .007 takes off 1cc for milling ls style heads. The more compact the combustion chamber, the more you have to cut to lower the chamber cc.

You could get the 243s down to 60ish ccs by taking off ~.035. with stock flat-tops, youd end up just into the 11s for compression ratio. Bringing your quench to .035 - .040 should be done ( .035 with hypers, tight bore, .040 with the forged pistons) should stop detonation. Just get a good tune for it, so it can live.