Back in the leaded days---when even Laifman was young---I always used unleaded
Amoco
93 octane premium as did all the gearheads except those who had ultra high
compression (they used Sunoco 260) I never had any valve seat problem despite my
abusive ways.
Al J.
Steve Laifman wrote:
> 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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