Best rear end gear for c4

[Kris 90]

What would be the best gears to put in the rear end with a c4? I’m fixing to have my rear axle rebuilt and I’m going to change from an open diff to limited slip. Currently I have 2.79 gears in it but want to know if it would be better to change that or keep it. As for the driving type it will mainly be city and hwy. I don’t plan on taking this car to the track at all but it will be driven spiritedly. I would like good acceleration and performance like my 2019 has if possible. 

[mustangstofear 608]

Go with 3:50 gears.

[Mike65 475]

1 hour ago, mustangstofear said:

Go with 3:50 gears.

I agree, my last Mustang was a 68 GT Coupe with a C4 auto & I installed 3.50 rear gears & I loved it.

[Kris 90]

That’s what I was think but wanted to know from people that have used that setup. Thanks

[barnett468 418]

22 hours ago, Kris said:

That’s what I was think but wanted to know from people that have used that setup. Thanks

if you like to drive 70 mph on the freeway for more than 30  minutes and do not plan to drag race anyone, you are far better off with 3.25 or 3.43. 3.50 is going to cause your engine to rev high on the highway plus it will burn a lot more gas.

 

[Kris 90]

I talked to a performance shop today and they recommended 3.0 gears due to the higher rpm’s at highway with 3.55’s.

[jmlay 80]

There several calculators available or you could. Real out the old Casio. :-)  Be mindful of the tq converter as well as where your engine makes it’s tq.  Remember tire diameter plays a part as well.:

https://spicerparts.com/calculators/transmission-ratio-rpm-calculator

 

[Shep69 149]

[barnett468 418]

21 hours ago, Kris said:

I talked to a performance shop today and they recommended 3.0 gears due to the higher rpm’s at highway with 3.55’s.

you will barely notice any difference between 2.79 and 3.00 gears and it will still have lame acceleration.

what engine do you have and what mods have been done to it?

 

[Kris 90]

I have a 302 with a mild build on it. Victor intake and Holley 750 currently but will be going with a Holley efi unit. 

[barnett468 418]

50 minutes ago, Kris said:

I have a 302 with a mild build on it. Victor intake and Holley 750 currently but will be going with a Holley efi unit. 

ok, then i would go with the 3.25 gears if you want a noticeable increase in acceleration but don't want to spin the engine fairly high on the freeway.

[Kris 90]

Thanks.