Hello all,

I know I jst keep coming up with more questions, but you guys provide the best answers! So I have a 1967 Mustang with a v-8 289 and a c-4 auto transmission. It currently has the really weak 7 1/4 inch rear end. I am upgrading to a Ford 9inch. I have decided to go with 31 spline as they are stronger than the 28 spline, and I have decided to go with a traction lock differential. My only problem now is gear ratio. It is a daily driver so I would like to keep some gas mileage but at the same time I want good power and would lean a little more towards the power than the gas mileage. Right now I am thinking either 3.50:1 or 3.70:1. Any thoughts or suggestions? If it helps anyone decide down the line will be a 351 Windsor and Ford AOD swap but those are at least a year off.


Thanks again!


-Andrew

 

If AOD is in your future, go for the 3.73:1 ratio. You'll get stout acceleration and good mileage in OD. You'll lose a little in the short run, but no use having 2 sets of gears around...or is it....

 

3.73 is not available for Ford 9"
3.70 or 3.80 is as close as you can get.

 

With the C-4 and a 3.70 gear the thing is going to spin like 3000/3500 @ 55. With an AOD it wont be as bad more like 3000 @ 70. So it all depends. Might not be a bad idea to have a couple of complete center sections laying around with a couple various gear ratio's, and with the 9" itll be a fast and easy swap.
-P.