12 volt Delco distributors (the ones with the tall cap and rotor) should be set at 28-32 degrees of dwell. The short cap models designed for 6V need 38-40 degrees for better magnetic saturation of the coil windings at the lower voltage. Changing dwell will have one of two possible effects on MPG- - - -"slim" or "none"!

Centrifugal and vacuum timing advance changes will make a huge difference. I've proved on dozens of dyno runs that one degree too much timing advance loses as much torque as 4 to 5 degrees of retarded timing from the "sweet spot" of maximum torque, so always err on the side of "not enough advance". My father discovered the same thing in the late 1940's when chassis dyno testing a 1934 Ford 3 window coupe dirt track race car.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
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