I'm at a cross roads here & want to ask you'll what you think. I sold my race car but I kept my 24" enclosed car trailer to store my Thunderbolt clone in & also have it to haul the car places if I want.
My truck currently has a 460 in it with 4:11 gears with a C6 transmission. The motor needs rebuilt & I'm debating on what to do. I've lowered the Dually & my wife wants to cruise in it more. I get 7 mpg's at best with the current combo. I have thought about rebuilding the 460 & put a higher gear in it, say maybe 3:54 gears. Or I have thought about rebuilding a 351w & putting a AOD trans behind it with say 3:73 or 3:55 gears so that I could cruise in it more & get better gas mileage but still tow with it. If I even tow something once a year now , I would be lucky. I'm really only going to be towing with the truck at tops less than 5% of the time I drive it.
What are your opinions? How many of you have Duallies with small blocks in them? How do you like them? With gas prices going higher & higher every week, my truck is staying parked longer & longer.

 

The 351 will do fine since you don't plan on towing much.

Have you considered how a big dually (probably crewcab?) truck would handle with an AOD and running steeper gears? It has a .667 overdrive gear.

You could run 4.56 gears and still turn nearly 1000rpms less compared to the C6 and 4.11's.

 

No, I didn't think about that. Yes, it is a Crew Cab Dually
Would it be best then to run something like a 3:73? Or then keep the 4:11?

 

Dually isn't really relevant for this comparison, as the weight difference is fairly minor. Just HP/torque, gearing, and weight.

I've towed with small blocks (302 and 351w) with 3.55:1 gears and with 4.10:1 gears. Typical weight is about 5000 lbs, though I did once tow more like 6500 lbs with a 302 and that just plain sucked. I could literally watch the gas gauge go down cruising on the highway.

In any event, most recent small block tow was 5000 lbs with a 351w and ZF5, though I towed the same load with the same truck when it had a C6. It sucked marginally less with the ZF5 but was still terrible. Your enclosed 24' with the thunderbolt and whatever else probably weighs more than 5000 lbs. My advice is to scrap the small block idea. You will not be happy. Also, an AOD will not last in a truck period, especially towing. You would be looking at ZF5 or E4OD (they make those for small blocks?).

I currently tow 5000 lbs with a mild 460 and ZF5 in an '86 Supercab 4x4 lifted on 35" tires with a Dana 60 swap up front. I get 10 MPG towing at 70 MPH, 2000 RPM. Not towing I get 12.5 MPG at the same speed. Truck weighs in about 6000 lbs so 11k lbs total. I would expect without the lift and bigger tires to get +2-3 MPG towing and not towing. For my normal commute (4 miles round trip) I get about 5 MPG. I'd expect more if it ever got to temp, but I have the choke on for half the drive.

My suggestion is to do a mild performance build on the 460 and swap in a ZF5. You can get better MPG out of it if done right. A small block would be a mistake for towing. it doesn't matter if you only tow once a year, you still tow and that is the deciding factor. I'd leave the 4.10:1 gears for now and see how much you can improve the MPG with a proper build and overdrive trans.

 

The problem with enclosed trailers is wind resistance at highway speeds.

 

I've been researching this build for towing/mileage on the current 460 I have for over a year. I've also been reading David Vizard's "Old " book "Performance with economy". I will be using a C6 because I hate changing gears all the time. I will probably use 3:54 gears even though I know they'll be sluggish on hills towing.
The only reason I've been thinking about the 351 & AOD is because of the gas prices & now that I've sold the race car I won't be towing regularly anymore.

 

An AOD will not last in a truck, much less towing. So throw that idea out the window right now. Limiting yourself to an automatic hurts MPG right off the bat being an automatic, and also limits your transmission options to either a C6 or E4OD. E4OD will require a controller to shift in an early carb truck.

Consider your fuel savings with 351w vs 460. What kind of MPG cna be expected with a mild performance build with either? I'd guesstimate about 16 MGP 460 or 18 MGP 351w, strictly highway. Around town the difference will likely be negligible. Driving 6000 miles/yr at $4/gal you're talking about a $167/yr savings, strictly highway.Double that MPG difference and you're still not talking much difference. Figure at least $2500 to build either engine if youre lucky and cna do it cheap... + maybe $750 for an E4OD and the controller... You're talking almost 20 years to break even before that thing starts paying for itself in fuel savings. We can adjust for inflation and projected fuel prices, but you'd still be well over a decade away from saving money unless you drive a LOT. Give some numbers on your city/highway percentage and miles per year and we can get some more accurate projections.

No matter which way you slice it though, going from 351w to 460 seems like a poor decision. You won't be as happy with the truck's performance, towing will suck, and you won't be saving any money for a long time.

 

A 460 getting 16mpg? I think that is stretching it, though 18mpg for a 351w is stretching it also. You are probably correct, the 351w will only get 2 or 3 mpg gallon more than the 460.

The c6 is a fuel mileage killer. The E4OD would be the way to go, but more expensive to install. I got 3 more mpg in my diesel going from a c6 to a zf, changing nothing else. I don't see any reason why a E4OD could not give you 2 to 3 mpg more either with it's lock-up converter and overdrive gear.

I think your best weapon is gearing. Your idea about the overdrive is a good one,, but like was said, the AOD is not going to hold up to towing. I would keep the 460, and put a E4OD behind it. Cruising, you will be in OD. Towing you will be in and out of overdrive depending on the load.

 

My guesstimates are running an E4OD with each, and pure highway. My '86 Supercab when stock height with 351w and C6 with 3.55:1 gear got ~16 highway at 70 MPH. It's not a stretch at all to get 18 with an overdrive gear.

 

Franklin2, what all do I need to do the E4OD conversion & where can I get it from? I can go with the C6 & Gear Vendors unit that my friend has as an option.

 

I just found out today that between buying the Gear Vendors overdrive from my buddy & buying what I need to convert it to my C6 it will cost me somewhere around $1200 to $1300.
I'm going to have to really think whether this will be worth it.
I might just keep what I have & put a set of 3:54 gears in it. I read somewhere that a Big Block gets it's best gas mileage at around 2200 rpm's & with the tires I'm running that would be about where those gears would put it.

 

Well how many miles do you put on it in a year and how much city vs. highway? How quickly would you like to start saving money from increased MPG? Need to know these to calculate your ROI and break even point.

 

I am assuming you are going to rebuild/restore the truck anyway is why you are asking these questions. If you are doing all this just for fuel mileage it will never pay off unless you really rack up the miles in a year.

You need to get away from the c6. Even with a gear vendors, it's not going to be as good as a E4OD for fuel mileage. It's that pesky torque convertor. It's always going to slip. If you get the rpms too low, the c6 torque convertor is going to slip even more. The lock-up convertor on the E4OD will drop your rpms another 200 rpm.

I have heard the best deal for a E4OD is the Ford dealer. They had a lot of problems with them when they first came out, but by around 1995 had it all figured out, and a Ford rebuilt unit has all these upgrades already in it. So you have the cost of the tranny, and figure around $500-600 more for a aftermarket controller. I know Baumann makes one, and I think there is someone else who also makes a controller for this tranny. It's going to cost you, but you will have a large tranny that will take what the 460 can dish out, and give you decent fuel mileage at the same time.

 

I have a almost identical truck, just an 86. E4OD will require a transmission controller, it is Electronic 4 speed overdrive. I towed a 10,000 lb 5th wheel for years with mine which came with 3.55 rear gears. Fuel "economy" empty was 10mpg, towing, about 8.5mpg except 1 trip into a 35 mph headwind keeping up with an RV convoy running 65-70 mph, I got 6mpg on that trip! Pulling power is good, it's not a drag racer, but doesn't do badly, empty, if you stomp it you can briefly light all 4 rear tires. I did put the early straight up timing set in it shortly after I bought the truck in 1994. If you are familiar with it, on Rt322W in PA, just below Centre Hall there is a stretch called 7 mountains grade, I topped it at 37mph in 2nd with the C6 and 3.55 gears towing that 5th wheel. FWIW a guy with the identical trailer, but towing with a Chevy dually and 454 with 4.10 rear was in 1st and 22mph on the same grade.

 

cadunkle, honestly, right now I hardly drive it because of the gas prices & how bad it is on gas. I want to drive it more & couldn't tell you all the specifics at this time.
I found Baumanns website a little bit ago. I'm going to look into this conversion & will let you know the prices once I find out.
85labaront2, Thanks for letting me know your results. This lets me know what I've been wandering about & gives me some results.