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Home Blog Blog 63 Automatic Cutlass 10.75 Compression?

63 Automatic Cutlass 10.75 Compression?

Home Page Forums Discussion Topics – Ask the Experts 63 Automatic Cutlass 10.75 Compression?

This topic contains 4 replies, has 2 voices, and was last updated by  jensenracing77 1 month ago.

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  • #13987

    jensenracing77
    Participant

    I was just informed and checked it with original documents but the 63 Cutlass engine with the automatic transmission got 10.75:1 compression? This is in more than one factory document. I had no idea of this and wondering how they got the higher compression? Or if this is a really big screw up in the publications department. I would assume that it is true because I have a 63 inspectors guide that has a specific code for the 10.75 compression engine. Then when I look at the 63 service manual it does not show a special piston for a 10.75 engine. I am confused by this and wondering how they got the higher compression if they did not use a special piston in the traditional Oldsmobile fashion.

    #13988

    JimNoel
    Participant

    Heads up,
    The compression in a 215 CID engine was changed with the size of the head cavity. The “volume” of a head is measured in cubic centimeters of liquid, usually water.The 10:75/1 automatic trans 1963 4 bbl engine has a 38cc head volume. The 4 bbl standard transmission and all Jetfire heads are 43cc or 10:25/1. The 2 bbl engines were all 51cc or 8.75/1. The exception is the export-low compression models. They were 8.25/1 for the 2 bbl and 8.5/1 for the 4bbl engines. Attached is the 1963 head numbers from my parts book and a chart for Piston/Rod/Compression ratio swaps for a 215 CID engine.

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    #13991

    jensenracing77
    Participant

    I had no idea that they had different heads. I thought it was only a dish piston for the 2 bbl and flat top with valve reliefs for everything else. I bet those 38cc heads are hard to find.

    #13992

    JimNoel
    Participant

    Heads up,
    Maybe, with the correct casting numbers and no, easy to shave the other 2 heads down to 38cc’s. The 10.75/1, ’63 heads, shouldn’t be too hard to find, they made over 100,000 of them!

    #13993

    jensenracing77
    Participant

    I know you can mill them to that but I would not think the factory done it that way. Not sure how much would need milled but it could require shorter push rods.

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