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compression ratio

Discussion in 'Race 400/430/455' started by Bernie Steffen, Jan 28, 2006.

  1. Bernie Steffen

    Bernie Steffen Well-Known Member

    How do you compute compresion ratio? I always figured divide the cylinder voume in cc"s by scombustion chamber volume in cc"s. Would Really like to hear the answer to this one, thanks in advance. Bernie Steffen bstef@mchsi.com
     
  2. 70 gsconvt

    70 gsconvt Silver Level contributor

  3. Thumper (aka greatscat)

    Thumper (aka greatscat) Well-Known Member

    Heres how I do it
    You need the following info
    head combustion chamber cc
    deck height
    piston cc
    gasket thickness
    bore size

    With our buicks the known values are
    455 bore= 934 cc
    455+.030=946 cc
    455+.038=949 cc
    .040" gasket=10 cc
    .020" gasket=5 cc
    for every .004" the piston is in the hole figure 1 cc,so a .036"deck is 9 cc
    Now lts do a sample calc

    say we have a 455+ .030"overbore= 946 cc
    usind a .040" gasket = 10 cc
    the piston cc is 33,typical 71 piston
    deck is .044"= 11 cc
    and combustion volume is 68 cc

    add all the volumes 946+10+33+11+68= 1068
    now this is the volume your compressing into the area above the piston,add those volumes 10+33+11+68=112

    now divide this volume into the total 1068/112=9.54 CR
    hope this helps
    gary
     

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