I currently have a 4-speed no overdrive with a 3.50 rear gear. At 70 mph I am turning 3,000 rpm. I am installing an AOD auto with a .67 final drive and want to switch to a 4.56 rear gear.

If I am doing the math right that puts me at 2,633 at the 70 mph mark.

4.56 divided by 3.50 = 1.31 x 3,000 = 3,930 x .67 = 2,633 is this correct?

 

Math is correct. I get 2619 but this difference is due to rounding 4.56 divided by 3.5 to 1.31. I used 1.3029. You are correct sir.

 

I hate math. Gear Ratio Calculator

 

Wont the tire size have something to do with rpms at 70 mph?

 

Thanks for reply.

 

Yes it does, but I am not changing tire size so it won't factor into the gear change.