Which head gasket is the best for the Olds 455 with aluminum heads?

Cometic vs FelPro

Some claim the FelPro seals better while the Cometic can be finicky with sealing.

 

The Cometic gaskets offer a wider range of thicknesses vs Fel-pro.

 

Haven't had any issues with Cometics, but my machinist also follows their surface finish guidelines. As noted above, the thickness options are nice to have.

 

My machinist said he prefers the Cometic but the head and block must have a fresh surface. If not resurfaced he said he would not use them.

 

Worth the money on a fresh build, and you can fine tune the compression ratio for more power.

 

We used Cometics on our build

The Block deck from the original condition it left the old Mondello shop was ok, and the heads by Vortecpro were beautifully finished with a fine RA.

I use this permatex copper spray a gasket on every set of MLS (Stock and Cometic) gaskets that I have ever ran and never had a single problem. Can you run the cometics dry and without that copper spray? Sure, but do you really want to take the thing apart because you didn't use it?

I have used Cometics and factory MLS gaskets on some pretty rough shape Subaru turbo builds and some good running LS engines, and they didn't leak, again, I have always used the copper spray a gasket linked below:

https://www.permatex.com/products/ga.../?locale=en_us




Needless to say, on our 455 build, even using 7/16 head bolts and making 600+hp, there was no head gasket issue and I don't expect one in the future if we add some more power naturally aspirated, with Nitrous, or some boost.

We were able to use the thinnest off the shelf Cometics at .027, to get our quench set right at .039 because our pistons were .012 below the decks.

 

Stock or near stock build? Just use Felpro.
Cometic MLS gaskets can seal better and resist failure, but they need a good smooth surface finish. So they're great for a performance and especially high compression (but not high enough to warrant o-ringing).