I though I had my build all figured out but now I'm starting to doubt myself. My truck is a 3/4 ton 4x4 with a D60 in the rear and a high pinion D44 up front - or at least it will have when I'm done. The rest of the powertrain will be an approx. 300 HP and 400 ft./lb. fuel injected 347 inch small block and a ZF 5-speed with a .76 OD ratio. Transfer case is a divorced NP205. Tires will be no bigger than 32". The Dana 60 has 3.73's in it now and I originally figured that would be about right. The front axle has 3.55's and I had planned to change them to 3.73's to match the rear. The truck will be used for basic pickup truck duty with occasional trailer duty hauling antique tractors. I'm starting to second guess myself on the 3.73 choice and am wondering if a 4.10 would be a better choice. I'm afraid it will end up being a slug with the 3.73's and the trailer on. On the other hand, I'm pretty concerned with fuel economy also. Gas isn't going anywhere but up. I'm afraid the 4.10's would eat me out of house and home. I really want to be able to afford to put some miles on this thing and am shooting for 14-16 MPG on the highway with the truck empty.Thoughts or experience with a similar rig?

 

I've got a 4 cylinder truck with 4.10s and things are great until you start running over 70. The revs start to stack up quick. That said, for that motor, it works fine.

Check out your combinations here:

Novak Conversions - Gearing & Gearing Math for Jeeps

3.73s, 32 inch tires and 4th gear in that ZF give you 2350 rpm at 60, right about tractor hauling speed.

At 70 in 5th empty you'll only see 2083.

You've got a low first and a low reverse, and a low range in your TC if you get in a real pinch.

I vote 3.73s.

 

3.73s sound about right, but I'd be more concerned about the engine. 347s aren't known for durability mostly due to the extremely short pistons. Typically, the wrist pin holes are covered with a plug so the oil ring can cross it, and they burn oil at fairly low mileage especially when worked hard.
A good set of heads on a 351w would give you similar numbers, and be more robust.

 

I appreciate the opinions, guys. I've thought all along that 3.73's would be about right. I think maybe I've been spending too much time in the rock crawler forums where the motto is always "Never fear the gear." I had an F-250 with the 4.9L, same ZF 5-speed, and 4.10's. It did OK, but it liked fuel and seemed just a bit strung out on the interstate at anything over 70 - even with the OD. Since the 3.73's are already in place, I think I'll put the truck together without a front driveshaft or changing the front gears and just drive it and use it awhile to see how it does. If the 3.73's provide enough performance and I'm satified, then great. I'll only have one axle to re-gear. If not, well, good used 4.10's and carriers are cheap and plentiful for both axles.

As far as the 347 goes, the piston and rod technology has come a long way. Those old short-lived and oil burning 347's are a thing of the past. The kit I'm going to use has slightly shorter rods that pull the wrist pin out of the ring lands. They've also got offset wrist pins to improve the rod ratio. These things are reliably running well past 100K these days. I had originally planned on running a 351W, but this truck is a '52 and the engine bay is a little on the tight side. The 351 would have fit, but I was running into a few clearance issues with various things. The tighter 302 package makes my problem areas go away. The 347 also has smaller journal diameters. That means lower bearing speeds and parasitic loss from friction. The stock truck 5.0L EFI intake that I'm going to use also flows quite a bit better than the 5.8L piece does. It weighs less. The 5.0L core I'm using has a roller cam and the 351W didn't. The list goes on. Can you tell I've put some research time and thought into this?!?