[Mad Max]

FWIW, below is a pic of a tow truck I built a long time ago. It was a 74 P-Wagon, with a fresh 413 and a 727, and 3.54 gears, and standard dually tires (235/85R16s I believe). Anyway, it got 7 mpg whether it was towing or not, and would cruise at 75 mph all day long. It had plenty of power for any speed, and would tow anything I wanted. It had dual gas tanks and I had plenty of range.

No matter what you do your fuel economy will not be awesome. I didn't care what my fuel economy was - I cared that the truck and the load would 'get there', and man it sure did. That 413 was fuuuunnnnn .

So, while I think your 440 will be just fine humming along at a few more rpms, I think if you were to re-gear the truck to 3.54s you would gain the extra top end speed you're after, and with the 440 you'll have the power you will need to push through the air. Youe fuel economy won't increase - likely it'll go down, but good fuel economy isn't the main reason you have that truck...is it

here's my old truck, "Frank" -

 

[treeslayer2003]

i will only put in these two more cents........i have 73 d100 2.70 rear gear 8-3/4 727, 360 with J heads and 800 T quad. it would smoke the tires with out using the brake and got about 18 mpg.
it is flat here, but i have never had any issues with any dodge trans running hot on the road if it was full of fluid.
i have never had a doggie dodge except a slant six. every one i ever had would at least bark the back tires, so i can't relate to you boys saying they are slow or doggy..........maybe its because its flat here and i'm near sea level.

 

[crazzywolfie]

i have messed with the numbers in the past and even re-gearing and running larger tires together would most likley cost about the same or maybe more than installing a overdrive transmission into a older truck and the overdrive transmission will most likely get you the best result since you already have 4.10 gears. i know i got 3.23 gear in my truck with 235/75r15's and i am still running about 2000rpm at 50mph which is where i most likely get the best fuel mileage. lets just say fuel mileage in it sucks. i don't know what rpm my 93 runs at at 50+mph but according to the calculater on grimmjeeper's website it should be turning at about 1425rpm at 50mph in overdrive with 3.55 gears.

 

[dodge82273]

install a constant variable transmission , some 2.70's and be done with it ? I don't speak for everyone , but I replace tires more often than I do transmissions or differential gears ....
keeping the motor at it's peak torque cannot be all that efficient or why is there 8-6-4 motors so on highway where you use the least power , it drops out cylinders ..... ( no,I don't like the older ones that do that ) ?

 

[treeslayer2003]

install a constant variable transmission , some 2.70's and be done with it ? I don't speak for everyone , but I replace tires more often than I do transmissions or differential gears ....
keeping the motor at it's peak torque cannot be all that efficient or why is there 8-6-4 motors so on highway where you use the least power , it drops out cylinders ..... ( no,I don't like the older ones that do that ) ?

we had an olds "short star" what a POS that was..........i took it the sale and felt bad that a friend bought it. he sold it and did ok.........maybe his conscious is better than mine.

 

[dodge82273]

yes , they did redo that thinking again , this time its better but still has to have drag from dead cylinders ,  even if they do hold valves open ... ?

 

[85 Royal SE Prospector]

i will only put in these two more cents........i have 73 d100 2.70 rear gear 8-3/4 727, 360 with J heads and 800 T quad. it would smoke the tires with out using the brake and got about 18 mpg.
it is flat here, but i have never had any issues with any dodge trans running hot on the road if it was full of fluid.
i have never had a doggie dodge except a slant six. every one i ever had would at least bark the back tires, so i can't relate to you boys saying they are slow or doggy..........maybe its because its flat here and i'm near sea level.

Perspective. Same folks that can be paranoid about losing torque and having too high a powerband then "upgrade" to a motor with the same/less torque at a higher peak and a higher HP peak. They get adequate and preferred mixed up. No, you don't need a 1 ton dually Cummins to tow a 15' boat or a Dart on a trailer- a 1/2 ton even with tall gears can do just fine or people would've never bought them.

So, while I think your 440 will be just fine humming along at a few more rpms, I think if you were to re-gear the truck to 3.54s you would gain the extra top end speed you're after, and with the 440 you'll have the power you will need to push through the air. Youe fuel economy won't increase - likely it'll go down, but good fuel economy isn't the main reason you have that truck...is it

I still find the idea that steeper gears in a truck can ever improve fuel mileage completely strange and am skeptical of the mathematical capabilities of any who claim such things. In cars I've only ever seen pretty severe drops in fuel mileage from steeper gears- like go down from 25 on the road to 19, 19 to 17. Now of course all that said, carburetor adjustments being off can absolutely murder fuel mileage worse than about anything. In the end, you can only really make sure it's like how you want it and does what it's supposed to and fuel economy will be what it is.

 

[Mad Max]

I still find the idea that steeper gears in a truck can ever improve fuel mileage completely strange and am skeptical of the mathematical capabilities of any who claim such things.

I didn't say 3.54's (in place of 4.10s), in this case, would gain fuel economy. I said that 3.54's (in place of 4.10s) will gain top speed for the same rpms, but will likely decrease fuel economy because of the aerodynamics at the higher top speeds.

Bottom line - if you can put the truck on a chassis dyno and determine where the power curves are in the engine's rpm band, you'd ideally want to design the chassis so that the engine is near its peak torque curve when the truck is at it's intended cruising speed. IOW, if the truck makes peak tq near the 2700 rpm mark, I think if you install gears or an overdrive so that the engine will be at that rpm at your intended cruising speed (where the truck and engine will be spending most of it's 'time'), I think that will likely net the best performance and fuel economy, regardless of whether you are towing heavy or empty.

 

[dodge82273]

Highway speeds do not require anywhere near peak power though , so I'm still confused , but thanks for trying to enlighten an old fool  anyway

 

[Mad Max]

I never said it was required, I said it would be the most efficient considering pushing a giant brick through the air at 70 mph will require some power, and since these trucks are not efficient to begin with, I am trying to help the PO develop a good efficient plan for his truck, at those speeds under stated circumstances. 

 

[KThaxton]

I still find the idea that steeper gears in a truck can ever improve fuel mileage completely strange and am skeptical of the mathematical capabilities of any who claim such things.

If a vehicle is geared too high it will be inefficient. Engines aren't efficient when they are lugging and vacuum is low. Geared too high, and the engine lugs more of the time, thus, lower mileage. Keep in mind, we are talking about a truck that is geared too high, vs. one that is geared properly.

In my experience, I went from 3.2's (with 33's) to 3.9's and my mileage was identical, but, I had much more power/torque and much better overall drivability. If I had 35's or bigger, perhaps at that point I would have gained some mileage by swapping to lower gears.

 

[treeslayer2003]

.......but i think they are efficient. my friends with ford or chevy trucks geared about the same get the same or less mileage than i do and many of those trucks have over drive where mine does not.
i cannot agree with some of you about lower gears getting better mileage.....they will not, i have had both. unless your towing a very heavy load up hill alot, the higher gear will do better. now we are not speaking of a serious trail rig here, but a daily driver i assume.

 

[SuperBurban]

It all depends on the torque curve of the engine.

Only new vehicle I ever bought, was a 1981 D150 shortbed, with the slant 6, 4 speed overdrive. I bought it to replace my 73 D200, that I converted to 4wd, by using a 78 chassis. it had a 318/435/203 combo. My old 73 got better mileage then the 81 by 2 to 3 MPG. I found myself driving the old 73 more then the 81, so when my sister and her family returned from Germany, I gave it to them.

 

[KThaxton]

.......but i think they are efficient. my friends with ford or chevy trucks geared about the same get the same or less mileage than i do and many of those trucks have over drive where mine does not.

Unless I am misunderstanding you, you are contradicting yourself in that statement. They have overdrive (which is an overall higher ratio) and they are getting the same or worse than you. Thus proving that lugging, at lower rpms doesn't always equal more efficiency. However overdrive is kinda-sorta not the main issue with a discussion of gearing as that is only one gear, where a lower or higher R&P ratio effects every gear.

Having too high of a ratio R&P also means that you engine has to work harder getting the load to move from a stop. Lower gears....the engine doesn't have to work as hard, this equals more efficiency.

i cannot agree with some of you about lower gears getting better mileage.....they will not, i have had both. unless your towing a very heavy load up hill alot, the higher gear will do better. now we are not speaking of a serious trail rig here, but a daily driver i assume.

As I attempted to make very clear, I (and I assume anyone else making similar claims) am referring to a vehicle that is geared too high vs one that is geared properly. Too high could mean simply that the tires are too big for the ratio or too high for the amount of work (towing) that is expected out of the vehicle.

Many people forget, or don't know, that not only do lower gears (or we could say properly low gears) put the engine at a higher, more efficient rpm, but there is also the torque multiplication factor that is even more important.

 

[treeslayer2003]

Unless I am misunderstanding you, you are contradicting yourself in that statement. They have overdrive (which is an overall higher ratio) and they are getting the same or worse than you. Thus proving that lugging, at lower rpms doesn't always equal more efficiency. However overdrive is kinda-sorta not the main issue with a discussion of gearing as that is only one gear, where a lower or higher R&P ratio effects every gear.

Having too high of a ratio R&P also means that you engine has to work harder getting the load to move from a stop. Lower gears....the engine doesn't have to work as hard, this equals more efficiency.

As I attempted to make very clear, I (and I assume anyone else making similar claims) am referring to a vehicle that is geared too high vs one that is geared properly. Too high could mean simply that the tires are too big for the ratio or too high for the amount of work (towing) that is expected out of the vehicle.

Many people forget, or don't know, that not only do lower gears (or we could say properly low gears) put the engine at a higher, more efficient rpm, but there is also the torque multiplication factor that is even more important.

you are correct, some are over geared. i was comparing 4.10 to 4.10 but the newer ones have OD and get the same or worse.
it won't be popular but i will bet if i had 3.50 gears in my work truck i would get much better mileage.
in the half tons i prefer 3.21 or better yet if its a 4x2 2.90 or 2.70.
i know you guys run big tires and do alot of trails, but that type set up is not ideal on the highway with 235s.
by the way, if any one close has a set of 3/4 ton rears in the 3.50 range..........

 

[KThaxton]

it won't be popular but i will bet if i had 3.50 gears in my work truck i would get much better mileage.

and I would agree with that.....assuming you have stock tires and aren't pulling a lot of weight around because your combination would be.......you guessed it "properly geared"!

Remember, nobody said lower gears always equal more mileage, but if you are geared too high (due to tire size or load), you might gain some mileage with lower gears.