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I am in the final stages of a frame off restoration a '74 Bronco for my brother, and I need some suggestions. It is going to have some 31" tall tires and a 4" lift. It has the original 302 with a 268 H cam, Performer intake, Autolite 4100 and Headman headers. It has a C-4 with an un-determined stall speed. What would be a good choice? It has 3.50 gears front and rear. I want to know what a good gear will be with the 31" tall tires. I don't think the 3.50's will cut it as it will probably be gutless on the low end. I am thinking 4.11's, but I wanted to see what anyone else thought. It is pretty much going to be driven on-road with an occasional trail ride. It will be primarily driven on the freeway to my bro's work, so the RPM's will have to be reasonable.
 

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If you plan on staying with 31s, the 4.10s will work good, but really, anything from a 3.73 to a 4.10 would be good. 3.50s are just a little high.

My truck has 35s most of the time with 4.88 gears which isn't quite as low as it sounds. When I have 33s on it, it's a little low, but with 35s it works good.

http://www.offroaders.com/info/tech-corner/reading/mph-rpm.htm
This will get you started. Remember a automatic with a non lockup converter will slip a little at cruise RPM, so take that into consideraton.

http://www.s104x4.com/Content/TechArt/javacalc.htm
 

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I also think the 3.50 will work fine with 31's to me it wouldn't be worth the time and money to change them out. I run 4.10 in my 74 bronco and run eather a 33,34,35 inch tire and its fine. I think with the 4inch lift though it won't take long before he wants some 33's
 

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Like already said, the 3.50 will be nice all around with 31" tires. I run 4.11 with 35" tires and at 73mph im at 3000 rpm's. If you want to drive it on the highway i would put in 3.73's even with a 33" tire you still have nice setup.
If its for street driving mostly and for fun go with 4.11 and a locker.
 

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I have a 74 with 31's and 3.50 gears, and it is a good combo. I have a 351 in it now, but when it had the 302 it was still a good combination.
 

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hey F-15 you're just down the road a bit from here. It won't be long before you'll be wanting 33's on your Bronco. I'd drop the cam down a notch and run a tighter converter for those steep downhills when you come to the AZ "sky islands".
You can keep your gears with a lower grunt cam and you'll have more than enough torque off-road in low range.

The short wheel base 302 Bronco is probably one of the best off-road rigs ever designed.


Bob
 
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