RE: Gas milage vs rear end ratio

[Earl Helm <earlh@xxxxxxxxxxxxxx>]

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The "Sweet Spot" is usually defined by where the torque and horsepower
curve cross, or
very close to there based on frontal area and vehicle weight.

Earl


Sweet spot indeed. If you mix the right cam, intake, carb, timing,
transmission, gear, and tires you can get pretty decent mileage. Putting
a lower gear will actually improve mileage in the city but hurt you on
the highway, with the exception of when a lower gear puts you in the
"sweet spot" on the highway. The "sweet spot" is where your cam, intake,
etc are making the most power with the gas they're burning. If you keep
your RPM in that range by adjusting gears and shift points, you'll get
the best mileage possible. Or you could run 4.56's and leave clouds of
smoke in your wake. Both are just as fun.

Dave Casey

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My personal experience went like this... I replaced the std 7 1/4 2.94?
in a /6 Duster with a 3.23 8 3/4 and GAINED mpg! The Duster had a mild
Crane cam and shaved head with porting.My theory is that the rpm
increase at road speed put the engine in the "sweet spot"Granted, this
was a low HP engine,but it was more fun to drive,and got more mpg.This
may not hold true with an engine that already has a good power to weight
ratio,the experts will know.Remember all the gadgets and trinkets in the
old J.C. Whitney catalogs??? If you installed all of them and added up
the % gains, your car would actually PRODUCE gasoline by saving more
than it used! It is a fine line to find the ratio that will work the
best for mpg,keeping the engine at it's "sweet spot" Too high of ratio
will require more throttle to keep enough torque to maintain the desired
speed,thus,more fuel consumption.Long flat road hill in the
distance?Slowly get your speed up,ease up on the throttle as you start
to lose speed. Stan "El Cheapo" Clinton

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