Originally Posted by chevybayboy

I've been searching in and and but can't seem to find the answer I'm looking for, well I'm getting ready to get my ls1 346 built with my 243 heads so I think my compression is around 10:1 or 10:2 I want to bump it up to around 11:1 or close to it without milling my heads I was thinking running a thinner head gasket with forged domed pistons what do you guys think? Oh and I want to be able to still run on pump gas say 91-93 octane

Originally Posted by KCS

First of all, and this is just bugging the crap out of me, in your sig it should be BRIAN not BRAIN.

Second, it takes a little bit of math to figure out compression ratios but luckily there are several online calculators available to make it easier for someone to determine what they need to do to achieve their ideal CR (static or dynamic). Wiseco, Diamond, Probe, etc all have their catalogs online so you can pick out a piston, plug in the dome volume into a calculator and determine whether it will meet your goals or not.

Lastly, why don't you want to mill the heads if forged piston are an option?

Originally Posted by bozzhawg

That should be no problem, just watch your dynamic comp and pay attention to how much your piston comes up out the hole/ deck height for your quench.

What you are trying to do is very common.

Originally Posted by 1bdbrd

With the right timing 11:1 won't be an issue. A friend of mine runs just under 13:1 on his 408 on 91. His is due to cam timing bleeding some off.

For you, I think the LS6 came stock with 11:1 compression?

Originally Posted by wildcamaro

Ls6 heads raise compression over ls1 heads, something like 10.8:1

Originally Posted by bozzhawg

Get the short block assembled.
Measure your deck height and how much the piston comes out of the hole. Or you can have your machine shop verify and measure this. I do it myself tho.This calculation will help you determine what head gasket thickness you will need to run for your desired quench estimation along with your static and dynamic comp calculations. Once I know how much the pistons are out the hole, I can kind of figure out what thickness of gasket I will run for quench.

A lot of guys do it backwards, they fixate on a certain static comp and at all cost buy headgaskets and mill heads, but never fully know how much that piston is coming out of the hole, they just guess and are surprised when **** goes bad later after the install.

Once I know the piston deck height clearance, piston dome, idea of head gasket thickness, quench, then I can figure how much I need to mill for the certain static comp. To figure your dynamic, you will need the IVC on the camshaft timing events, ICL, LSA, and duration.

Mill the heads last. You can always measure but once the heads are milled, your stuck with that unless you buy another set of heads or run a thicker headgasket but then that may throw off your quench and drop static comp.