Re: Highway speeds/engine rpm/ gearing and other stuff

Posted by PackardV8 On 2013/3/31 22:28:52

For NON OD gimme da axle ratio and the overall tire diamter u want to use and i'll calculate it.

Or try it your self:

Multiply tire/wheel OVERALL diametner by 3.1416. Call the answer to that calculation "C".

Divide 63,360 by C. Call that "M".

Multiply M by the axle ratio. Call that "S".

S will equal the engine rpm at 60 MPH.


THen divide S by 6 and that will give the incremental engine rpm for EACH 10 mph of car speed.

From post 1 of this thread the axle is 3.96:1 ratio and the wheel tire combo diameter is 28".

Multiply 28 by 3.14 = 88" ("C")
divide 63360 by 88 = 720 ("M")
Multiply 720 by 3.96 = 2851 ("S") THe engine rpm at 60 mph.

Divide 2851 by 6 = 475 rpm FOR EACH TEN mph of car speed.

SO at 30 mph 3 times 475 = 1425 engine rpm.
at 60 mph 6 times 475 = 2850 engine rpm.
at 70 mph 7 times 475 = 3325 engine rpm.