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Compression Ratio/Head Decking?

Discussion in 'The Garage' started by bonanza, Nov 2, 2004.

  1. bonanza

    bonanza Registered Member

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    Hey, I previously thought I had a 1979 400 in my truck, until looking at the casting numbers on the heads and the block, it shows to be between a 1971-1973. The heads are 997's which came with 74-76 chambers. I was wondering what the compression ratio is, and how much should I deck these heads to bring compression between 9:1-9.5:1? I'm thinking between .020-.025, anybody know?
     
  2. 84_Chevy_K10

    84_Chevy_K10 Banned

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    The correct term for head machining would be called, "milling" not "decking." Decking is done to the block's deck surface.

    I'd suggest decking the block to zero to gain compression rather than milling the heads.

    To figure compression you'll need to know what kind of pistons you have.
     
  3. bonanza

    bonanza Registered Member

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    I am not going to machine the block under any circumstances. The pistons are stock cast dished pistons. It might be called milling the heads in your neck of the woods, but where I'm from everybody refers to it as decking.
     
  4. m j

    m j 1/2 ton status

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    you have to measure everything
    specs mean nothing

    you deck a block
     
  5. rcamacho

    rcamacho 1/2 ton status

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    You might want to give Dave at http://www.flow-technics.com/ a call. He just set up my BBC 402 with milled 454 heads to bring the CR back to 9.2. I'm very satisfied with the work. BTW, if you mill the heads you will also need to have the intake manifold hand fitted/milled to fit and probably require shims under the distributor housing to keep the shaft from bottoming on the oil pump drive.
     

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