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Compression ratio

Discussion in 'Chevy Trucks' started by ratplow408, Jan 3, 2005.

  1. ratplow408

    ratplow408 Member
    from PA
    Messages: 33

    I recently built a BBC 396. It was bored 60 over with 21 cc domes on pistons.
    The block deck height is 9.780. The heads are closed chamber, rectangular port, they were cut 10 thousandths. I bought a set of oval port open chamber truck heads with 116 cc combustion chambers. My question is if I get these heads done, how much will it lower my compression ratio? Is there a formula to figure this out. The closed chamber heads have 106.9 cc chambers. Any help would be greatly appreciated. :D

    p.s. current compression ratio is 9.2:1
  2. wfd44

    wfd44 Senior Member
    from Maine
    Messages: 369

    Yes volume of the cylinder including combustion chamber and head gasket with the piston at bottom dead center dvided by the cyilinder volume including combustion chamer and headgasket with the piston at top dead center = compression ratio. There is no easy way.
  3. ratlover

    ratlover PlowSite.com Addict
    from IL
    Messages: 1,325

    its pretty easy to figure out. I had a compression ratio calculator on my computer that would do dynamic or static but I seem to have lost it. do a serch on the net for compression ratio calculator. I lost he formula so I'm no help......

    try a place like chevelles.com they are a pretty good board or were when I frequented there
  4. PackRat

    PackRat Member
    from Kansas
    Messages: 47

    I used these to work out the details on a 327 build I'm planning.


    The answers I got there match petty well, with the answers I got from some friends that race.
  5. The Boss

    The Boss 2000 Club Member
    Messages: 2,099

    I've got a 396 bored .060 over for sale if anyone is interested.
  6. ratplow408

    ratplow408 Member
    from PA
    Messages: 33

    Thanks for your help guys. I'll check out these sites. Still waiting for snow here in S.E. Pa.