Fordnatics List Archive

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Mail From: (email redacted) (George Chang)

Hi Everyone,

I have another naive question for the Fordnatics... How can
I tweak my timing for maximum gas mileage? I'll be taking my
'84 Crown Victoria copcar (351W, 2 VV carb, AOD, 2.7X rear end) to
Southern California when I attend my son's graduation.

It will probably be my last long drive for some time, and
I'd like to see just what kind of mileage I can get (I'm not going
to break any speed or acceleration records, so I thought I'd go for
mileage).
So far I've installed vacuum gauges on the manifold and
venturi, and I find that driving style affects both readings
considerably. By keeping the manifold vacuum as high as possible, I
was able to average 24.7 mpg on a 200-mile trip at about 60 mph.
But now I wonder if tweaking the timing would help a bit.

What do you think? I notice that the vacuum advance can put
20 or 30 degrees of advance onto the ignition.... should I adjust
the vacuum advance diaphragm spring rather that the base timing?

Thanks!
George