head gasket thickness

[coupe32]

When I had some machine work done on my X heads for my 340 I used head gaskets that came in a rebuild kit. They appeared to be steel and appeared to be pretty thick. I didn't think much about it but since have learned that there is probably a thinner head gasket I should have used to keep the stock compression. My question is how much compression have I lost if I used a thicker head gasket? Is it worth the trouble to change the head gaskets? This engine probably originally had thinner head gaskets than the ones I used.
I guess I need some input on what thickness the stock head gaskets were or how thin I can go to boost my compression or at least get it back to where it was.
This is a mostly stock 68 340 engine except for the cam, headers and intake. I am running a fairly mild Racer Brown cam. Thanks

[John Kunkel]

The original factory gasket is a single sheet of embossed steel, if the replacement gasket is composite (several layers) it will be thicker by nature.

Without knowing the exact compressed thickness of the replacement gasket it's impossible to compute the compression difference.

[ehostler]

Thinner head gaskets are more prone to failure. With that being said, Cometic head gaskets can be purchased with the correct bore size and in a variety of thickness'.

For a mostly street engine. The compression difference won't gain you much at the strip. At most, expect .05 off your time.

[coupe32]

It doesn't sound like it will help that much to make a difference. I just wondered if I lost that much using a thicker gasket. The car is not raced and it does run pretty well as it is. I think I'll leave it alone. Thanks for the info.

[bandit67]

I read in the Chrysler small block book the the tool and dyes that made the original thin metal head gaskets were destroyed long ago. I can't remember the exact story but, they decided that a thinner gasket than what is presently made would be useful and teamed up with a prominate maker to make one as thin as possible and be trouble free. I forget the part number but Mopar Performace books have them listed. I got mine from Summit and they were about $45 bucks for the pair. At the time my local dealer could not tell me it they were 42 each or a pair. They come as a pair.
Most kit gaskets are in the .038 to .042 range and compress down to .034 -.0036 installed. These are .028 and compress to .25-.26 installed. I am running them on a 318 and 360 with no problems and plan to use them on a higher compression 340.
Don't think I would pull the heads off a good motor just to change the gaskets, but I would keep a set on hand . I think the part number is P4120094 and will give you a 1/2 point compression change over a .040 gasket.