Stan:
Actually, if you look at Richard's table carefully, you will see
that a 1974 head starting at 3.550 thickness, and ending at 9.6:1 CR
with a 0.020 overbore (which is what I did) should be milled to 3.416
which is 0.134" thinner. I had my head milled .120", plus had the block
decked 0.010", which takes the effective head milling to 0.130", which
is within 0.004" of what Richard recommends.
I milled my head based on measuring the volume of the chambers
with a burette, and that is how I came up with 0.120". It was gratifying
to see that my measurements agreed so closely with Richard Good's
numbers.
The 0.080" number that Roger Williams mentions is based on a
starting compression ratio of 8.5:1 (?).
Vance
-----Original Message-----
From: 6pack-bounces+vance.navarrette=intel.com@autox.team.net
[mailto:6pack-bounces+vance.navarrette=intel.com@autox.team.net] On
Behalf Of Foster, Stan
Sent: January 05, 2008 7:36 AM
To: Derek
Cc: 6pack (6pack)
Subject: Re: [6pack] Compression Ratio Calculation
Thanks Derek, that is quite a formidable spreadsheet !.
And that thickness is consistent with Roger Williams who says in both
TR6
books that the US head will need about .080 removed to bring the
compression
back up to 9.5:1
According to Richard (zero decked, standard pistons) 3.5 - 3.416 = .084
for
9.5:1 CR
Less than I was expecting.
Vance once told me he had .120 removed from his 74.5 for a target CR of
9.6:1
but he did not totally zero deck the block but left it .010 above the
pistons
so I guess that would account for some of the difference between .084
and .120
(the more volume between the piston and the top of the block, the more
you
have to remove from the head to get the same CR ?)
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