I used them with lots of nitrous in a pro streeter,not one issue!

Several companies make multi layer gaskets including Fel Pro.

Where do I find the acceptable compressed thickness figure?

they come in different sizes

One good thing about cometic gaskets is that they handle detonation really well. I was running 10.2;1 compression on my engines, and the detonation actually damaged the pistons before the head gaskets.

These things are good !

What Cometic told me was, If the gasket is suppose to have a .040 compressed thickness, if you measure them uncompressed with a dial caliper, you need to get at least .050 to .055. I did not spend much time quizzing the guy since I had new ones and it did not matter. If this is something you want to do, give Cometic a call and hear what they have to say first hand. That call I made was over a year ago, so they may not recomend that any more. I still would not use them over.

One of the keys to having all the time success with Cometic head gaskets is to make sure the block and head surfaces are correctly finished , free of nicks and gouges or scratches and to make sure you use a good cleaner like alcohol or such to clean both surfaces before assembly and make sure you do not get carried away with head bolt thred sealer-lubricants that will squish into the gasket seal area when installing. Also inspect the viton(black) coating for gouges, abrasion and such because it is this coating which actually fills in the tiny voids in the surfaces when the gaskets are torqued. Proper torque in proper pattern in at least three steps is also advised. We have been using exclusively Cometic head gaskets for over three years on all our 496 engines and kits without one failure or problem. They are in my opinion definitly the best head gasket for marine use. Yes we do use them over on the dyno motors several times and checking the uncompressed height is a must when you do this.

Ray @ Raylar

Did we come to a consensus regarding the need to retorque after intial run in period? Always needed to do this on new conventional style fel-pros.

If you have properly torqued the Cometic head gaskets once , thats all they will ever need.

Ray @ Raylar

I've heard nothing but good things about Cometic gaskets. They are the latest technology but I think they've been around for several years but were used primarily in race bike applications. I've noticed lately that now Mr. Gasket and Fel-pro are making the MLS gaskets as well, at competitive prices.
I agree with Ray that particular attention needs to be given to the finish of the deck and heads.
The Cometics actually come with instructions which tell you that the finish needs to be like 5 ra (I think its 5). Ra is basically the smoothness of the finished surface. I not sure what method is used for this so talk to a machinist/engine builder. I recently read an article on the new Fel-Pros which indicated that the Fel- Pro gasket require less of a smooth surface because they coat the outer layers with Viton which fills in minute surface imperfections. I also noticed that the Fel-Pros are made of Stainless Steel layers. I'm not sure about the Cometics. Anyone know whether the Cometics are stainless? I have a set that I'm hoping to use in salt water so I'm thinking the stainless is the better way to go.