I've always used a composite, but I've cracked a head, and bought a cheap set of 76cc '70s heads as a temporary replacement, and I'd like to try to raise the CR a tad bit, so I figure a thinner head gasket would be good. Has anyone used a steel head gasket before? do they leak easily? that's my biggest concern, I really don't want to have a leak...

the one I was looking at:
http://store.summitracing.com/partde...art=FPP%2D1094

 

I'm running a .015" felpro steel shim gasket in my car and haven't had any leaks. I did have my heads milled flat to be sure it sealed.
Later,
Charlie

 

the differance in compression is very small. shim gaskets are harder to seal. i'd run a coated gasket, around .021 i think thick. if i were to run a shim i'd only do it with the deck and head surfaced.

 

I'd have to disagree with ede...the shim gaskets make a noticable difference in compression....from going to a standard .041 or .039 gasket to a .015 you gain .6 - .8 points in compression....the difference between 9.5 and 8.7 would be very, very noticable and significant! The smallest composition gasket that I know of is .026 and even then you would see .3-.4 increase.

 

Using a shim over a composite gasket wount do much of anything except be more prone to leaking and blowing out. Unless this block has been machined perfectly flat and the heads sufaced I wouldent even bother. Last couple builds I did were lower compression, there was no loss of power and being able to run crap gas with more advance netted quite a gain over a high compression engine with premium fuel and less spark advance.

 

I have always run shim style gaskets, just like the factory did. In factI try to buy GM gaskets. Running a coated versus a shim style gasket can make a noticible difference in compression.

The coated FEL PRO gasket (PN 1003) has a compressed thickness of .041" giving you a volume of 9.1 cc. The embossed shim gasket (PN 1094) has a compressed thickness of .015" giving you a volume of 3.3 cc.

If the engine is assembeled with the thick gasket (and 64cc heads, real flat tops and zero deck clearance) the CR works out as below:

(4 x 3.14 x 3.48) x 15.625 = displacement in cc's = 682.95

Add the combustion chamber volume to displacement, and divide by combustion chamber volume to get CR:

682.95 + 9.1+64 = 756.05 / (64+9.1) = 10.34:1 CR

If you run the same formula only changing the head gasket volume you get:

682.95 + 3.3 + 64 = 750.25 / (64+3.3) = 11.14:1 CR

Thats an increase of .8 compression points which is substantial.

As foor leaks I have never had one, and I have never had excessive work done to any of my decks / heads. As long as the suface is clean, not banged up , and the heads are torqued properly the shim gaskets seal as well as any other. GM used them for over thirty years with out too much trouble.....

 

The only thing that I would add to that is the the thinner the gasket, the more vital the flatness of the head/block mating surface. If you go to a machine shop they should have a list of compressed gasket thickness for you so you can run some numbers ahead of time.