i am trying to find out what gears will be most efficient friendly with the driving conditions....i would like to find out the rpm at a certain mph with different gears and in 5th and 6th

3:73
5th at 65 mph=rpm
6th at 65mph=rpm
5th at 70mph=rpm
6th at 70mph=rpm
3:89
5th at 65 mph=rpm
6th at 65mph=rpm
5th at 70mph=rpm
6th at 70mph=rpm
4:10
5th at 65 mph=rpm
6th at 65mph=rpm
5th at 70mph=rpm
6th at 70mph=rpm Thanks for the help!!!

 

ttt

 

Assuming your car is equipped with the stock (RPO QLC - Z-rated tires) 245/50-16 (25.65") tires - remember, the stock tach typically reads 100-300rpm higher than actual rpm:

3.42
5th at 65 mph = 2,156rpm
6th at 65mph = 1,457rpm

5th at 70mph = 2,322rpm
6th at 70mph = 1,569rpm

3:73 (Multiply 3.42 rpm's by 1.091)
5th at 65 mph = 2,351rpm
6th at 65mph = 1,589rpm

5th at 70mph = 2,532rpm
6th at 70mph = 1,711rpm

3:89 (Multiply 3.42 rpm's by 1.137)
5th at 65 mph = 2,452rpm
6th at 65mph = 1,657rpm

5th at 70mph = 2,641rpm
6th at 70mph = 1,784rpm

4:10 (Multiply 3.42 rpm's by 1.199)
5th at 65mph = 2,584rpm
6th at 65mph = 1,746rpm

5th at 70mph = 2,783rpm
6th at 70mph = 1,881rpm

I'll move this post to "Drivetrain", where it belongs.

 

4.10's are a good choice for an M6 without much modding. Even with 4.10's, 75mph is about 2,000rpm in 6th and a SBC will run for months at that rpm/load.