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Home Blog Blog Compressed thickness of stock steel head gasket

Compressed thickness of stock steel head gasket

Home Page Forums Discussion Topics – Ask the Experts Compressed thickness of stock steel head gasket

This topic contains 7 replies, has 3 voices, and was last updated by  joe_padavano 2 weeks, 3 days ago.

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    Does anyone know what the compressed thickness is of the stock steel head gasket? The FelPro head gasket is .040 to .042 and I know the originals were thinner than this. I want the original compression on my 4 speed car and if I use the FelPro gaskets I will have to mill the difference off the heads. I would rather not mill them at all but I really want the 10.25 compression.

    I also have a set of NOS head gaskets but don’t really trust them if I don’t have freshly machined surfaces, this would end up with to much compression.



    The 1963 Oldsmobile Parts manual lists 1961-1963 F-85 head gaskets at 0.020″ thick for all 215 cid engine applications. These gaskets are all steel, #578813.
    The automatic transmission Jetfire’s are 10.25:1, and the manual transmission Jetfire’s are 10.75:1.
    If you had 0.020″ milled off the head to clean up the surface, the FelPro 0.040″ should give you the correct compression ratio?



    I did not know the parts book give the thickness. I had not looked these up. As far as compression, I thought I read it was only the automatic 63 Cutlass that had the higher compression? That also confuses me because I can’t find anything in the parts book that is different for them to gain that compression? Did they have special heads with less cc’s? I have not looked up the heads yet.



    OK, Just found it, It has a separate part number for the 4bbl heads of the 63 manual trans and the 4bbl heads of the 63 hydromatic trans. Looks like the Jetfire all have the same heads so I believe all the Jetfire would be 10.25



    Yes, you are correct. The compression ratio difference is between the 1963 4bbl carb auto 10.75:1 & manual trans 10.25:1. All Jetfires were 10.25:1
    A copy of Dan LaGrou’s head listings attached



    Very cool, I never seen that document before.



    Attached is the NHRA spec sheet for the 215cid.



    Keep in mind that the NHRA numbers are the minimum blueprint spec, not the as-cast numbers. I’m not sure about the 215 heads, but later iron Olds V8 heads tend to run 2-4 cc larger chambers than the NHRA blueprint numbers in the as-cast state. Obviously this also depends on how much the head has been surfaced, how much the valves have been cut, etc.

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