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Discussion Starter #1
Want to swap my 243s 64cc heads, with some LSA heads 68-69cc.
I'm wondering how thin of a headgasket I can go, in order to keep the compression up, before running into PTV clearance issues.
I have a theoretical number from my calculations. but anyone have real world numbers? what gasket thickness do you use?

I rather not mill the heads, and readjust the compression via the headgasket. I'm currently running LS9 .051 thickness gaskets on on my LS2.
It's a twin turbo E85 car if that's relevant. it's going to be an apples to apples swap, so my only concerns is the gasket.
 

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The Entenmann's Shim-Sham
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It depends on how much your piston is coming out of the hole. Is it .005", or has the block been decked before and it could be .010"? That will determine how thin of a head gasket you can run since you want to maintain a .040"-.045" quench area. However, you aren't going to gain much compression through the head gasket, since you're talking, at most, a decrease of .010" from stock, compared to milling the heads .030".
 

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Discussion Starter #5
It depends on how much your piston is coming out of the hole. Is it .005", or has the block been decked before and it could be .010"? That will determine how thin of a head gasket you can run since you want to maintain a .040"-.045" quench area. However, you aren't going to gain much compression through the head gasket, since you're talking, at most, a decrease of .010" from stock, compared to milling the heads .030".
I guessing milling is the more popular question. if people are milling .030, theoretically, switching out my .051 to a .036 or .040 should be more than adequate. I'm just trying to get a general consensus there, as i'll be checking clearances before hand
 

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I guessing milling is the more popular question. if people are milling .030, theoretically, switching out my .051 to a .036 or .040 should be more than adequate. I'm just trying to get a general consensus there, as i'll be checking clearances before hand
You should just mill the heads.
 

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same logic applies, still will needs number to calculate.
Still will what?

.007" mill per cc of chamber volume is the general rule. There are compression calculators online, it's not hard to figure out.

Just an fyi, one measurement that is hard to find is "top ring down" which is the measurement between the top of the piston and the first ring. It's approx .182" on a stock piston.

The rest of the numbers you can find yourself.

 

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The Entenmann's Shim-Sham
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I guessing milling is the more popular question. if people are milling .030, theoretically, switching out my .051 to a .036 or .040 should be more than adequate. I'm just trying to get a general consensus there, as i'll be checking clearances before hand
So, LS engines typically have the piston come out of the hole by .005"-.006". I would not go thinner than .040" for the head gasket. However, you need to verify how much the piston sticks out at TDC before buying the gaskets. That's the only way to know.

Also, keep in mind that you will need to also verify piston to valve clearance after milling.
 

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I was in a similar boat with mine. I’m running 823’s, and didn’t want to mill. i’ve got .040” thickness head gaskets and +4cc dome pistons. they do have valve reliefs though, can’t remember how deep. no clearance issues.

on another note, have you thought about flycutting? what kind of como ratio are you after?
 

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Yep, my LS2 has them from the factory.
i’d be surprised if there was a clearance issue with .040” gaskets, anything beyond that I wouldn’t know. flycutting might do the trick if you wanted to go thinner, but i’m not sure how the hypereutectic pistons would hold up.

i’m interested to hear about what you end up running !
 

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Discussion Starter #16
I plan to shove all the boost through them, I rather not remove head material, if I can accomplish my goal with a gasket. You can't unmill a head
 

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what is with this not wanting to mill?
normally I am pro milling heads, but this application might see boost. At that point I can swap gaskets (probably get rid of the +4cc pistons as well) and keep the same heads. I admit that milling is a better way to increase compression, but I just didn’t want to buy another set of heads down the road. my other n/a setups have had milled heads.
 
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