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1412Re: The '49-'62 V8... anything out there?

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  • jvandecreek25
    Dec 9, 2004
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      --- In Cadillac_Performance_Association@yahoogroups.com, "Jerry
      Brown" <jerome@p...> wrote:
      > Thanks for the additional information re. 425 heads on 500 engine.
      Are the
      > differences in the combustion chamber so that I don't need to
      change out
      > valve train etc.?

      The late 500 heads have 120cc chambers, while the 425 heads have
      96cc chambers, this is where the increase in compression comes from.
      The 425 head has the same valve sizes, and the same intake and
      exhaust ports as the late 500 head, the factory did remove some
      weight by opening up the area where the push-rods pass through, but
      this change has no effect on performance or durability.
      Earlier '69-'73 heads do have better, more direct exhaust ports and
      work better on a race type engine, but the compression goes to over
      12:1 when used with the flat top pistons of a '74-'76 500(and 472)
      and these stock cast pistons are prone to disintegrating at those
      compression ratios, this combination is not at all streetable on
      available pump gas.
      So for "Bang for the buck",
      Install the 425 heads, use a 425 head gasket(can be an old used
      one) to locate the positions of the extra steam holes that will need
      to be drilled in the block deck of the 500, a 3/8" electric drill
      with the appropriate size bit is all that will be required, assemble
      the heads to the block using 500 head gaskets. no other
      modifications or non stock parts are needed.
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