Have a 89 f-350 crewcab 460 4:10 rwd dually that has the auto with over drive. I will be towing my 5th wheel 28 ft appx 9.000 lbs. About 1300 miles. Just wondering what speed would be best. I will be towing with the overdrive off. Just don't want to tax the motor by revving to high. 65 with over drive off it tacs about 3100. Fuel consumption is also a factor I am thinking about, it gets about 9 to 10 when i pulled a chev caviler and a uhaul car transport. Maybe 4000 lbs or less. and about 10 with nothing and overdrive on.

 

3100 rpm is very high for such a large displacement motor like the 460, it also produces its peak torque way below that, at 2k rpm. The E4OD is made to tow in OD, but if you still want to keep the OD off, stay at whatever speed is closest to 2k RPM, which will prob end up around 45. If you use OD, youll be at 2000 rpm right at 65

 

The E4OD is rated to tow in OD but you better make sure you get a trans temp gauge and the largest aftermarket trans oil cooler you can find before you tow heavy. With that done you should be fine towing in OD on flat ground at any speed you want to go as long as that doesn't make the trans constantly hunt for gears, if it's doing that you need to back off a bit.

 

the only thing turning od off will do,is use more fuel needlessly.
the gear hunting wont be very common with the diesel or the big block.that's more an issue with the 302/351w engines.if she doesn't want to hold od then speed up or slow down until it does.the 460 is already thirsty enough.

 

Agreed with the others. Personally I would NOT drive it out of OD.
If it starts to hunt for gears on hill, just bump it out of OD for the hill, then put it back in at the top

 

Thanks for all the help and info everyone. With the speed limit 80 on 90% of my trip i wont feel like such a hazard, if i can do 65 or close. First time pulling a heavy trailer or heavy for me. My last ford had the C-6 and never had to worry about it. 84 28' Newmar London Aire ford chassis E-350 auto 460 C6 4:10. 1990 f-250 xlt single cab 4x4 460 e40d 5 speed 3:55 only pulled a 12' 63 kencraft trailer loaded maybe 2500lbs. Thanks again all, having the truck serviced and the 7 pin put in only had the 6 pin in the bed And waiting for my fifth wheel rail kit to arrive hopefully out by the 13th. Snowed last 2 days here in Montana time to head to Texas and Arizona.

 

Where is there an 80mph speed limit?

 

Big beautiful Wyoming...on I80 in the middle of no where. Maybe parts of I25 as well. Likely on parts of I90 or I94 based on the OP's location.

 

I 90 Montana I 15 Montana,Idaho, Utah,and Nevada except major cities and where you go thru passes and curves.

 

Wow, And I thought 70 was high

 

I just have to clear up this misconception here, there is no way that's true for any gas V8. Maybe for a diesel 2000 RPM is peak torque, for the 460 its up around somewhere between 3500 and 4000. Why does engine crank up over 4k when you floor it? The shift points of the auto trans are set to give you the most out of the engines torque/horsepower. Also, torque is most useful for getting the load going, once you are cruising HP is a more important factor.

That said, 3100 RPMs is a very high engine speed for sustained periods. At that speed you would be lucky to get 5mpg and the 460 might overheat if your cooling system is not in excellent condition. I would turn on OD once you get up to speed if RPMs are that high. If the engine needs more power for hills or in a headwind it will sense the engine is bogging under load and upshift. Or you can just switch off OD in anticipation of a hill.

 

It's vice versa.
Torque is down low.
Horsepower is up high.

 

Wow I'm learning a lot here so glad that I joined this site. And yes I agree 80 is to fast in my mind but the cars today can do it. I do worry that its to fast for some drivers way more to anticipate and a lot of drivers are not skilled enough. Just a tire blow out at that speed can be devastating.

 

Towing at that speed is even more of a concern. What is the "truck" speed?

 

Warning, boring math lesson ahead.

MR KROGOTH already addressed the first error here, but I wanted to address this one. The idea that trucks need torque, not horsepower, is mathematically wrong. It is helpful to think about it that way, but it's still wrong.

Power equals torque times speed (mathematically, HP = ft-lbs of torque x rpm / 5252). So power is torque that's moving. If you have a lot of torque but no power it's like putting 140 lb-in of torque on a bolt that requires 150 lb-in to move: it just sits there and doesn't do anything. Once it's moving, then you have power.

Whether you have an econo box, a sports car, a pickup, a semi or a John Deere tractor, useable horsepower is what it's all about. It will take a certain amount of horsepower to do whatever work you are trying to do, whether that's accelerating, pushing into a head wind, going up a hill, pulling somethng heavy. Whatever. And it doesn't matter at all how much torque you have, if you have enough useable horsepower you can do it, if you don't you can't.

Where the saying "trucks need torque, not horsepower" becomes useful is in the concept of useable horsepower. A motorcycle engine might make 200 horsepower at 10,000 rpm. If you could run it in a pickup at 10,000 rpm it would definitely out-pull a 300 in-line 6 that makes maybe 150 hp at 3500 rpm. But letting the clutch out at 10,000 rpm isn't going to make for long clutch life, and if that motorcycle engine drops 25% of it's speed to 7,500 rpm it's going to lose a bigger percentage of it's horsepower than the 300 will dropping to 2,625 rpm.

That's what a low rpm torque peak gives you: a flatter power curve. You'll have more useable power at a wider range of engine speeds, so you won't need to have a 7 speed transmission and be shifting constantly to stay on your power curve. But it's the flat power curve that is actually helping you, it's still the horsepower that's doing the work.