My 355 build is getting close to being finished. Soon I will be ordering head gaskets and my engine builder recommended Cometic which I'm fine with. My question is the thickness of the gasket and quench height.

My build is as follows:
(All current intentions are to build this engine for NA only)

355 LT1 - Bored 4.030
SRP Forged Flat Top -5cc pistons
Zero Deck Height
Block has been line honed
Stock GM crank - turned and polished
Eagle 4340 Rods with 7/16 ARP bolts
AI 232/237 .580/.580 Hyd Cam
LT1 heads with 54cc chambers (Ferrea 2.0 and 1.56 Valves)
Cometic Head Gasket (4.110 opening) thickness undecided.....

Like many of the local engine shops, my builder hasn't seen too many 93-97 LT1s come through the door. He was surprised to see how much compression the LT1 could run with the reverse cooling heads, a bit concerned at times as well. He has questioned the compression the engine will have with concern that it is too high for pump gas. I insisted that I didn't want to lower the compression to the stock 10.5:1.

The static compression of the setup currently (if I use a .050 gasket) looks to be around 11.4:1 by using an online calculator. My builder recommended the .050 gasket. With the block being zero deck that would make my quench right at .050 as well. It is my understanding that the desired quench should be around .035-.045 to lower the chance of detonation and pre-ignition. If I drop to a .040 Cometic Gasket that would bump my compression a bit to 11.7:1 according to the online calculator.

So my main question is that thickness should I run? From looking over many other successful LT1 builds the 11.7:1 doesn't seem to high for pump gas granted everything else is in order such as fuel, tuning, cooling, ect.

 

Is the surface finish on the block and heads up to sealing Cometics??

Compression tolerance is influenced by cam.

The bone stock LT4 was 10.8:1, there are a lot of LT1s on the street over 11.5:1 and a fair number over 12:1

 

Personally I would go with the .040 gasket. I don't think you would have any detonation issues at 11.7:1 as long as like you said everything else is in order.

 

Yes the surfaces of the block and heads were done with Cometic gaskets in mind. The engine builder said from the beginning he strongly recommends using a Cometic gasket and asked me if I was OK with spending the few extra bucks on them. It was decided to go with Cometics before any machine work was done and my builder did the decking of the block and surfacing of the heads knowing a Cometic gasket was going to be used.

My main concern is having the compression too high.

 

You could add a FULL POINT and still be okay as long as the tune is in order.

I run a .033" Cometic and have static compression of 12.7:1 with no problems. You are well within the realm of running on pump gas - no problem.

If this isn't your DD and you're looking to squeeze everything you have out of it I'd personally go with an .030" (12.2:1) or an .035" (12.0:1) gasket. If it's your DD, I'd recommend the .035" gasket.

 

This isn't my daily driver, just a weekend car that will see the track once in a while. It will also be getting a dyno tune at a local shop on a Mustang dyno to ensure the tune is dead on.

I didn't know what was the minimum quench distance safely was. I also wasn't sure about heat expansion of pistons/rods at operating temps and what that did to the quench distance. I want to get the max out of my setup and don't want to overlook any of the details at this point. I realize that the machine work as to be dead on to run that tight of a quench. I will be checking the deck height of all 8 cylinders to be sure they are exactly the same before ordering the gaskets.