Tire size and Gear ratio will also come into play. I have ran different size tires and different gear ratios o my truck.
Started with 3.90 gears and 28 inch tires (275/60r15) with the original gmc 336 v8 and nv4500
Changed to 3.38 gears
Swapped 59 gmc motor for 59 pontiac 389 bored and stroked to 447 inches with tripower... The perches were ripped off the freshly rebuilt HO33 rear with 3.38 gears
Put a full floating 9 inch in with 3.70 gears and true trac posi. Worked great!
Changed the 275/60r15 tires for 31X10.5 tires... lost gearing and didn't pick up economy.
Changed gears to 4.30 with 31 inch tires. 4.11 gears would have been equivalent to 3.70 gears with 28 inch tires. Lost economy and seems geared a little low. 70 mph around 2500 rpm. The current combination should be able to tow a car or pull a boat out of the water. The difference between the 4.11 gears and 4.30 gears is about 120 rpm at 70 mph. On my motor with the long 4.25 inch stroke, slightly lower rpm is preferable. Small blocks tend to like rpm more than big blocks.
