Tom,
Quite a shopping list of 351 questions. Have you read Monroe's
"how-to..." book on the differences? This is an invaluable reference,
and even tells you the compression ratio with each different head on
different blocks. (see below)
You must be aware that Ford never did install "hardened seats", as does
a head that has inserts installed when larger valves are used. What
they did is to "flame harden" the existing cast iron seat with a high
temperature treatment to the exhaust valve seat only. I think they used
induction heating equipment that concentrated RF (radio frequency) waves
on the seat, not use a torch.
The change took place when lead was ruled out as an additive for gas,
somewhere in the late 60's. The 351W was introduced in '69 and had air
injection ports added in '75 (with smaller valves and larger combustion
chamber volume to reduce C/R.) This air injection system, for pollution
control, was not a blessing, and is not a good feature. It is even found
in '66 289's
An early 351W (60.4 cc chamber) would give 8.1:1 compression ratio on a
260, the later 69 cc version would give a C/R of 7.4:1 (pretty low),
without changes to the pistons.
The extra exhaust threads were for different manifolds. One set fits the
260/289.
If you have a head that was run for a while on leaded gas, the deposits
made allow the car to use unleaded gas on the non-flame hardened seat
with the deposits left by the leaded gas. That is how today's Tigers
can run on unleaded without changing the heads.
As far as compression ratio goes, forget about "milling the head", there
just isn't enough you can take off to make much difference. The only way
is to use different pistons. To see what too much compression can do,
consult with Steve Sage, who has a 351W.
Steve
____________________________
Steve Laifman
Editor
<http://www.TigersUnited.com>
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