DANMAS@aol.com wrote:
> As for improved gas mileage, in my simple mind I can't see how putting the
> transmission into OD will reduce the energy required to move the car down the
> road, and, since an engine is most efficient at its torque peak RPM, the
> mechanical energy required to move the car can most efficiently be converted
> from the energy content of the gasoline if the engine is operated near that
> torque peak, not at a relatively ineffecient 2500 RPM.
>
Thats at full throttle (highest efficiency at torque peak). At the power level
needed to cruise down the highway (probably 15 - 20 hp) the most efficient is
usually at lower engine speeds and greater throttle openings as compared to
higher engine speeds and less throttle opening. At the lower engine speeds
there
are less friction losses and more importantly less pumping losses (energy
required to pull the mixture in against the intake manifold vacuum). Also with
lower engine speeds the small amount of unburnt fuel is a smaller percent of the
total fuel used.
An overdrive will probably not increase engine life any measurable amount but it
will increase fuel economy and allow a more relaxed cruise.
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