Here's what I came up with in the wee hours of the morning. There was a lengthy series (back to back) of extremely noisy thunderstorms rolling through the Detroit area between 11:30 pm and about 1 am. The storms kept waking me up and then something happened to my brain--either the electricity gave it life (a la Dr. Frankenstein) or the roof was leaking and I am all wet. But this is what I came up with:

Based on my '95 F150 300 I6's torque curve (assumed correct by curve drawn from a web posting data and mnfr data) I calculated the following for a 70 MPH towing cruising speed to obtain maximum power (note the 2500 RPM with 3.08 is my current condition and the 145 hp is mnfr listed peak) (Please bear with all the "=" signs; they keep the columns from collapsing into meaningless garbage when I post):

RPM==REAR=HP=TORQUE=HP*TQ==C=====C*TORQUE
2500==3.08==124==260====32240==0.855===222
2750==3.39==131==250====32750==0.91====228
3000==3.70==138==242====33396==0.95====230
3400==4.19==145==224====32480==1.0=====224

NOTE: C is HP at given RPM divided by max HP (145)

So what does all this mean. Well, I was trying equalize the differenced between torque and horsepower. First I assumed that since HP is a function of torque and RPM and torque is a function of HP and RPM, that by simply multiplying them together I could get a general idea of where speed of work (HP) and work done (torque) are maximized and use that as the optimum towing rpm. As shown above then 3000 RPM at 70 mph should give the best power. Then I went one further and decided that, since hp is the speed of the work being done, that by adjusting the work done (torque) for the speed the work is done, I could compare torque adjusted for different work speeds (C*TORQUE) and take the peak number as the optimum power for towing. When I again got 3000 RPM it was encouraging; however, that likely is because C*TORQUE is a more refined version of HP*TORQUE. Thus I would be best off towing with a 3.70 (I think Ford has a 3.73) rear end. What I find interesting is that running at the peak HP would gain little over running near the peak torque (actually 265@2000) and would surely wear out the motor faster. Does any of this make sense? (I still am trying to wake up after only 4.5 hrs sleep.)

 

Go and get some sleep buddy.

 

Judging by the number of other responses to my post, I guess you're right.

 

I just didnt think I was smart enough to respond! Actually, I have some of my best ideas when I wake up in the middle of the night, but I forget them by morning!

Nathan

 

Maybe you should write a calculator program for this. That would be very helpful to some people.

 

One problem is that my whole analysis is based on a torque curve that may not be that accurate (mnfr data + internet data + variation between each engine + drawn in curve + reading points off of that curve). If one had their engine output recorded off a dyno then it might work out. I later tried to calculate rear wheel torque which should be greater in a lower gear because of the higher engine rpm. It seemed that the increase in rear wheel torque was dropping off above 3000 RPM, but it was not significant relative to the accuracy of my torque data. What we really need is some Ford engineers to comment on FTE. While I am at it, I still am puzzled by the mnfr rating the same truck about 2000 lb greater trailer hauling capacity with an auto tranny than a manual. I know this has been discussed before but I have not seen a convincing answer.

 

Tall order TallPual!
I must admit that you seem to be working this out mathematically and you may arrive to some conclusion.My suggestion is trial and error.While the math sounds good it may not be applicable in the real world.Work your rig at a rpm that it is comfortable(rpm stand point)then do the math to achieve the correct axle ratio to achieve that rpm at the speed in which you feel comfortable driving.

 

Like I said, the electricity must have done something to my brain that night. Right now I am towing at about 2500 RPM and 70 (indicated, but really closer to 68). It hauls really nice at that, but for the occasional head winds and steeper hills. I am thinking of an aerodynamic nose cone for the trailer, if I can find one somewhere. That should also improve gas mileage.

 

For the hills and headwinds add NITROUS!

 

The reason for the higher towing rating with the automatic has little or nothing to do with the strength of the tranny. It is simply due to the fact that clutch life is seriously impared by trying to get a heavy load moving with a clutch and current trans and rear end ratios.

Back when truck 4 speeds came with creeper first gears with a 6.5 or greater ratio and 3.55 was considered an economy rear, getting a load moving was no big deal. Today's trannies with a 3.5 or so ratio often combined with 3.08 or even 2.73 rears simply beat the clutch to death and the manufacturers want to avoid warranty expense. The obvious solution of a 6 speed with a creeper first would not sell in large enough numbers to justify its development expense.

 

StrangeRanger: Thanks. It makes sense that the clutch is the weak point and that also is what Mark Salem (http://www.salemboysauto.com/default.htm) told me in an e-mail. Trailer Life magazine back in '94 said this too.

 

Well first off sorry to spoil the FORD party but its time to get rid of that Ford and get something good. Try a JEEP product with the 4.0 L I6.

I have a 1994 Jeep Grand Cherokee with the 4.0 L engine. We have 180,000 miles on it and much of that has been spent towing 1 of 2 trailers all over North America. With a 3.73 rear end ratio it runs at about 2500 RPm at 60 mph. Everything still original and running like new.

Trailer 1) a 1975 FORD 3/4 ton missing its worst parts, the engine and cab. The box rear end and frame make a great utility trailer! This unit has been on several 1800 mile(1 way)trips to New York, Montreal etc.

Trailer 2) a 4,000 lb tandem axle cabin camping trailer. This thing is about 7' tall and 8' wide. This unit has been behind our JEEP all through the Rockies in Canada and the USA, the Badlands of North and South Dakota, Minnesota, Iowa, Maitoba, Saskatchewan, Alberta etc.

On all of our trips over the last 6 years we have never seen a FORD with 6 cylinder engine pulling any kind of load. You will see the odd Jeep Cherokee and Chevy Blazers though.

FORD in reverse -
D river
R eturns
O n
F oot

 

fitzdicksn:

The only way you will spoil the Ford party is like a wino would spoil a wine tasting event by walking in with a bottle of Mad Dog 20/20. The Jeep may do the job, but those who really know their trucks always prefer Fords.

 

TallPaul
Best to ignore the troll. Response only encourages his type. Let him find a Jeep site where he belongs.

 

You're right StrangeRanger. I'll exercise more restraint in the future.