1412Re: The '49-'62 V8... anything out there?
- Dec 9, 2004--- 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 tochange 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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