so i am thinking about upgrading my gears from the stock 2.79:1 just for that little bit extra umph i do drive alot on the highway but i am gunna be rebuilding my 8in soon so i was thinking like either a 3.25:1, 3.40:1, or a 3.55:1 rear ratio i have a c-4 with a 289 that is kinda stock i am putting cam in real soon but i want some help deciding

 

well, IMO,anyting over 3.50 is too much since the 3rd gear is only a 1.00 ratio, your gas mileage will go to hell. I thought about swapping out my 3.25 out to maybe 3.50 or 3.70, but with the torque my pony should be putting out, i think I'll be ok with the slightly better gas mileage instead. If you dont mind a few more bucks on gas, go with something like the 3.55. But if you expect to have some decent torque and your somewhat happy as it is now, than stay with something lower like the 3.25.

 

+1 what billybob said, i just posted this link in another thread, u might find it helpful also, http://www.csgnetwork.com/multirpmcalc.html

 

i was thinking the 3.25

 

I'm thinking overdrive is even better...

 

3.55



i have a set i got from summit for an 8 inch that i will put for sale soonif someone is interested

 

For a 65/66, a 3.25 rear would be good since they have a shorter tire than the later Stangs. If you don't have much highway driving, don't be afraid of the 3.55's, however.

 

its my 67

 

i had 2.79's with an open diff in a 8in, but i just finished putting a 3.55 posi unit in, and was only able to take it for a few test drives to break it in so far. There is a big difference, and i like it alot, it really jumps off the line. I have a 302 with a C4. I havent taken it on the highway yet, but i am hoping to do that today and i will let you know how the gears are on the highway.
Matt

 

Rear gear selection is governed by engine performance. Since you have a stock engine and you are putting gears in now, but make it sound like you want to add more power to your engine later, what is your long term goal for the motor, that way you won't do the rear twice.