CamaroFreak87

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

Insomniac92z28

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

ede

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.

AllGoNoShow

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.

SSC

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.

littlebagz

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.....

blacksheep-1

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.