IGNANt

iTrader: (15)

I was told to go with Cometic gaskets for my setup and I found a couple: 3.905/.045 and 3.910/.040. .040 is the stock thickness right? but the stock bore is 3.905? Id like to know which one would be right for my setup and why:

-LS1 Block
-249/254-.617/.619-112lsa
-Polished GM Crank
-Probe UltraLight 6.125" Forged I-Beam Rods
-Ross 3.905 Forged Pistons -4cc
-Total Seal Advanced Profiling Rings
-200 shot plate system

JPH

iTrader: (2)

What does your combustion chamber measure across the head?

smask04C5

iTrader: (1)

Stock bore is 99mm, which is 3.8976. I used 3.910 Cometics .040 thick as you described. Stock head gaskets are approximately .056 compressed.

The Alchemist

iTrader: (19)

The difference in diameter is only 0.005" which is only 0.0025" at each side of the bore. I don't think that it would make much difference, I say go with the tighter quench, thinner gasket as well.

CW 99 Z

I would run the 3.910 bore gaskets. You dont want the gasket the exact same size as the bore. Esp on ls motors where the piston is out of the deck.

Sales2@Texas-speed

iTrader: (5)

It really wouldn't make any difference on 99.5% of the builds on this site. We stock the 3.910" bore gaskets from Cometic at competitive prices. Let us know if we can help!

Gary Z

My recollection is that the stock LS1 gasket diameter is approximately 3.940 inch - it is definitely greater than 3.910 inch.

vettenuts

iTrader: (4)

You need to know chamber width and taper width on the top of the bore. Then you need to get the fire ring about 0.030" outside. I say none of the above until more information is provided.

JPH

iTrader: (2)

You should have just quoted me Bob? LOL

PREDATOR-Z

Yes, aggreed with Vettenuts and JPH, and there is also another thing you need to check, you PISTON DECK HEIGHT. It is an aftermarket block, pistons could be .010 out and with .040 could be too tight a quench at .020, then you might need thicker gaskets.

Find out what is your piston position in/out of hole, then make your decision .030 circle bigger than your bore.

IGNANt

iTrader: (15)

its a stock block with an aftermarket forged rotating assembly, the heads are 853 casting milled to 62cc.

PREDATOR-Z

Ask who built it what is your piston deck height. If it is you, then measure it.