Kerry its hard to tell for sure if the higher rpm or the lower works better,
because there are competing factors. At the lower rpm, the torque converter
will slip more (I assuming we are talking about an Imperial towing), and
converter sippage equals energy loss. The engine however is more efficient at
the lower rpm high load setting. Of course, this is a carburated engine, so
its possible that the mixture is richer at the low rpm high load, hard to tell.
In an injected car, as long as you are not in the enrichment level, it should
be more economical to be at the highest possible load at the lowest possible
rpm.
No, maximizing vacuum does not improve gas mileage. In fact, operating the
engine under vacuum is very inefficient by itself, as during the intake stroke,
the piston "fights" the vacuum (that's one of the reasons diesels are more fuel
efficient, they do not operate with a throttle that creates vacuum).
The fact the engine is more responsive at the higher rpm does not mean its more
efficient operating condition. FOr example, at 70-75 you can cruise with
second gear, and it will be far more responsive if you floor it, but there will
be little argument on the effect on gas mileage.
You could install a flow meter to measure gas flow. That would tell you the
most efficient condition. It would not be cheap though.
D^2
Quoting Kerry Pinkerton <pinkertonk@xxxxxxxxx>:
> I have a question about fuel mileage. Will running with the RPM on the
> lower side of the torque curve (about 1800 rpm) when pulling heavy (as
> in towing) be worse on mileage than shifting down so the RPM is up in
> the fatter part of the torque curve (about 2500). At lower RPM the
> motor seems to be lugging when towing while at the higher RPM the motor
> seems more responsive and it SEEMS like my foot is not as close to the
> floor.
>
> If I put a vacuum guage on the car will that show me the best operating
> conditions for max mileage? Does higher vacuum = higher mileage? This
> is one case where one of those instantaneous mileage computers would be
> handy....
>
> Kerry
>
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