^^^its a 7 layer gasket specifically designed for boost. Im no engineer so thats my best answer!!!

 

Just a stock LS1 gasket.

 

So far I'm having great luck with 0.040 cometics on my 370. It's a little over 10:1, and currently only turned up to 15 psi with my S484.

The block is zero decked to the JE pistons, so I'm right at 0.040 quench. I went 4.060 bore gasket on my 4.030 bore iron engine. So far so good, probably not turning the boost up until the warmer weather.

Doing this with stock 317 heads. I have nicer valves in them, but they're just stock chambers/decks/ports.

 

Ok good to know.

I went .045 simply because the stock pistons come out of the hole a little and I didnt want it too tight.

 

My LS9’s have seen 18psi so far on my 370. Doesn’t anyone make a good MLS gasket smaller then 4.1” bore?

 

Yeah, I think most stock pistons on gen 3 and 4 engines are 0.010" out of the hole at TDC. Since I've got forged everything that geometry was different and we zero decked it to them.

I'm also running ARP head studs to hold the heads down. I haven't had any issues at all at 15 PSI, there's just no point in turning it up until I do suspension work and get sticky tires, so I haven't seen if it's OK above that yet.

 

I would get a gasket that sits closely to the same bore, otherwise you are building a hot spot in that area. Thats how i see it, you essentially have an area of open air around the outside of the cylinder.
BTR has the COMETIC 4-BOLT MLS HEAD GASKETS. You choose which bore you want and how thick from .030-.060 thats what i would do.
I ran the LS9 gaksets on my 5.3 under boost with no issues but i just went with everyone said to do.
Just my 2cents..

 

There is no downside to the gap formed by an oversized bore head gasket, save for perhaps a little more tensile stress on your head fasteners. That is assuming you don't care about passing emissions...that sort of crevice volume can be hell on hydrocarbon emissions. It isn't a hot spot either, in fact it is extremely cold in the crevices.

Run whatever gasket that works and you're happy with...just don't tell the EPA.

 

Thanks Jake.

I hope the cometics hold up.

 

My LS9's saw 21 PSI. No leaks, but 2 rods appear to be shorter than the rest...