I have just purchased and milled a set of 243 heads .030 to go on my 2003 Silverado 5.3. I have dished pistons so that is the reason for milling. I am confused however on what head gasket to run. I was just gonna get the stock replacement fel-pro mls HG from oriellys or autozone, but I would like to go thinner around .040 for more compression. Can anyone recommend a good head gasket to run. I hear people recommending an LS1 or LS2 or LS6 gasket, but the cylinder bore size is different than the 5.3 so I am confused. I feel that you would lose compression from the head gasket bore being bigger? Or am I wrong. Thanks in advance!

 

Cometic makes an .040

C5788-040

The factory L33 with 799/243 heads use the same bore size gaskets.

 

Do u mean the LM7? His truck is the same as mine and I have the LM7. And I thought 799/243 heads didn't come stock on trucks til 07? Or am I misinformed? Idk it's 138am and I'm tired lol

 

No I mean an L33. It's an aluminum 5.3L. It uses 4.8 pistons and has 799/243 heads from the factory.

They had 3 different 5.3L's for the silverado depending on the year.

LM7 standard 5.3L
L59 basically the same long block but flex fuel capable.
L33 high output 5.3L - 2005-2007 extended cab 4x4 only

when they switched to Gen 4 engines in the GMT 900 platforum is when you got 799/243 standard on the 5.3L but the RPO codes were different.

https://en.wikipedia.org/wiki/LS_bas...l-block_engine

 

learn something new everyday lol

 

Yeah I found the cometic on summit, but my concern is that the thickness is good at .040 but the bore is 3.910 and my cylinder bore is 3.78 that's a 0.130 over bore. Wouldn't the over bore of 0.130 cancel out the compression I would gain from the thinner gasket. The stock replacement fel-pro gasket is 0.051 thick and 3.835 bore. That makes a lot smaller over bore at 0.055. I've always read that some overbore is good but anything past .060 on the gasket will cause you to loose noticeable compression.

 

Gm runs a gasket like that on the L33. I believe it's to compensate for the larger combustion chamber.

GM part number 12589226 is a single 12498544 is a pair.

They use the same head gasket on the 5.7L LS1

 

You would have to look at a compression calculator that takes that into account.

Cometic will make you a custom set in any bore size and thickness you specify.

 

Called Cometic and I had them make me a set. .040 compressed thickness and 3.810 bore, that's gonna make some nice compression. Wasn't cheap lol $180, but you gotta pay to play I guess. 🙌🏻

 

Sure do!!!

I ordered the last pair summit had in stock of the C5788-040 a few weeks back.

I noticed the date keeps getting moved back on when they will be available...