What gears for my tow van

[FAT CAT]

I've got a 78 E-350 van that I'm turning into a 4x4 camper & sometimes tow van. I just rebuilt the 460 motor and 3 speed C6 transmission and now I'm trying to decide on the gearing for the diffs.

This rig has a Dana 60 rear and Dana 44 front and and a 205 T-Case. It has 4.10 gears in it now, which worked with the 33" tires. I'm moving up to 37" MT/Rs and I'm thinking 4.88 gears will be good but maybe 4.56 will be better for gas millage???

One thing that surprised me with my Explorer W/ 5.13 gears, is when I went from 37" tires to the 40" tires my gas millage improved by a good amount.

I've been driving around with 36" military tires for a couple months & with the 4.10 gears the gas millage has been horrible. What's throwing me off is the 3 speed transmission, what gearing do you think will be best? I want some 4 wheeling grunt in the low range but I need to squeeze the best millage out of it on the hwy. when towing.

 

[IZwack]

I guess this depends on the terrain you're driving in (mountainous vs. flat). But my vote is for the 4.88s if the 4.10s were killing the mileage.

 

[MountaineerGreen]

I am sorry, but 37's and a 460 I can't really see getting good mileage What did you get with 33's and 4.10's?

 

[Lefy]

the 460 is a torque monster and the c6 has a 1:1 ratio for 3rd gear
and getting good mileage out of a 460 with a three speed is going to be a challenge.

saying 33s with 4.10s worked well
with 33s and 4.10s you should be around 2720 at 65mph
37s with 4.56s you be at 2692 rpm at 65mph
37s with 4.88s your at 2881 rpm at 65mph

staying with your 4.10s and throwing 37s on your at 2426 rpm.
which is going to give you the best fuel economy on the highway, and you won't have to re gear, I think the 460 should be able to spin that. and the added diameter of tire is whats going to give you better mileage.

I based my info on this chart that shows engine rpm at 65mph with a 1:1 ratio in the trans.
The chart is divided into three categories.
Blue = Towing power and acceleration
Black = best overall drive ability.
Yellow = best fuel economy for highway

the article
http://www.4wheelonline.com/superlift_tiresize.htm

 

[FAT CAT]

I am sorry, but 37's and a 460 I can't really see getting good mileage What did you get with 33's and 4.10's?

Yeah, it's never going to be good, I need "as good as it gets"

When I got it, the guy had put some cheap 31's on it, so I don't know how it did before I put the 36's on.

I'm just looking for the best I can do without overdrive in the tranny, It's only going to tow about 4 times a year.

It's going to spend most of the time as a Baja family camper, exploring the desert and the remote beaches.

 

[FAT CAT]

the 460 is a torque monster and the c6 has a 1:1 ratio for 3rd gear
and getting good mileage out of a 460 with a three speed is going to be a challenge.

saying 33s with 4.10s worked well
with 33s and 4.10s you should be around 2720 at 65mph
37s with 4.56s you be at 2692 rpm at 65mph
37s with 4.88s your at 2881 rpm at 65mph

staying with your 4.10s and throwing 37s on your at 2426 rpm.
which is going to give you the best fuel economy on the highway, and you won't have to re gear, I think the 460 should be able to spin that. and the added diameter of tire is whats going to give you better mileage.

I based my info on this chart that shows engine rpm at 65mph with a 1:1 ratio in the trans.
The chart is divided into three categories.
Blue = Towing power and acceleration
Black = best overall drive ability.
Yellow = best fuel economy for highway

Thanks for that!

It would be nice to just leave them for now to see how the 4.10's do now that the motor and tranny are pulling like new; but since I'm going to be putting a locker in the rear, it makes sense to change the gears if I'm going too...

I'm leaning toward 4.56 now...