300 RPM Should I?

[JLC10756]

Hello everyone. I have a question to ask if I may.

My van, a 2014 Ford E450 V10 14800 gvwr with 4:56 rear end gets horrible mpg.
I'm used to getting 10mpg with many other vans I have owned, and I'm fine with poor gas mileage as I'm also a powerboat owner who's boat burns 35gph at 3000 rpm.

So I buy this brand new cut-away and have Forest River put the body on it. I fly from Connecticut to Forest River Factory in Indiana to drive home an empty Van. This is about an 800 mile trip. My first fill up equals 8.0 MPG.

This is an empty 12ft utility body box with a nice cab faring over the cab to blend the cab to the body.

Next fill up 7.75mpg. So for the next 800 miles I try all kinds of driving scenarios trying to find this vans sweet spot rpm/speed for the best mpg.

There is none. Now that she is loaded up to 13,000 pounds it gets a steady 6mpg. I'm living with it of course but I'm now considering a rearend change from 4:56 to 4:10. I calculate it will drop me 300rpm.
Im not great in math so Im having a hard time figuring out the MPG savings, but what I do figure (crudely) is about a .75mpg increase. So maybe I will get close to 7mpg if I change the rear end?

Can someone educate me on the pros and cons of a rear end change. I don't want to go bigger tires as I don't want to kill my brakes.

I tried a K & N filter but the van just laughed at me for the attempt.

How do you guys get your great MPG?

Thanks, cant wait to read the suggestions.

[BFlinn181]

The rear end will help, but you won't be first off the line at stop lights or accelerate to highway speeds quite as fast, not things you'll probably miss if you're trying to increase MPG anyway.

Whether or not your ECU will need reprogramming or not isn't something I can say, I don't know all the factors that it uses to compute shift points and the like.

I do wonder why such a rear end was put in your truck in the first place, perhaps to increase towing rating or something?

[twinboat]

If during your mileage comparison runs, your Van downshfted, it will downshift sooner. So unless your cruising flat ground i dont see a savings.

It takes a certain amount of horse power to move something thru the air at a set speed. You can't change that by lowering the RPM of the engine. It will still need to make that power.

What would taller tires do to your brakes that the loss of "engine braking", due to lower RPMs, not ?

[JLC10756]

Thanks all for your help.

The taller tires would increase top left to right sway and in my opinion wear brakes out faster because of more Tire diameter / leverage to stop the tires. I would do bigger diameter tires if I could increase my rotor diameters. Or... am I being to careful about the brakes vs Tire size deal?

Thank you.

[Skip426]

Welcome to iRV2.

Rear gear change , might not provide any increase in MPG, if the gearing means the rig won't pull a hill without gearing down, one even two gears.
If the gear change drops the engine out of it's torque power band , it'll live in a lower gear and your RPM, on hills will actually be higher.

Figure your fuel cost in , cents per mile , then IF ! , you do get the calculated increase in MPG , calculate the miles it would take to break even with the gear change cost; provided ; of course ;you get the increase you hope for.

[BFlinn181]

Originally Posted by JLC10756

Thanks all for your help.

The taller tires would increase top left to right sway and in my opinion wear brakes out faster because of more Tire diameter / leverage to stop the tires. I would do bigger diameter tires if I could increase my rotor diameters. Or... am I being to careful about the brakes vs Tire size deal?

Thank you.

How much of a tire size change are you contemplating? The cost of changing out 6 wheels and tires would be pretty expensive, as much or more than paying to have a new differential installed.

I don't think you'd do much to the braking by increasing tire size, unless you're going from 15" to 22.5" wheels.

[Skip426]

Originally Posted by JLC10756

.

Or... am I being to careful about the brakes vs Tire size deal?

Thank you.

JMHO: No . . Before I retired , ( 34 years at a Dodge dealership ) I'd get owner complains about stopping power/ handling / MPG, on trucks , finally convinced the service manager to ignore complains from customers with oversize tires. Tire stores would gladly install the the tires , but not explain any of the down side of the added , un-sprung weight, and leverage against the brakes.
Problem was very apparent until Dodge increased the , rim size from 16" to 17" to accommodate larger rotors and calipers, that helped unless the owner went over 1 1/2" taller on the tires, then they faced the same issues.

[JLC10756]

Originally Posted by Skip426

JMHO: No . . Before I retired , ( 34 years at a Dodge dealership ) I'd get owner complains about stopping power/ handling / MPG, on trucks , finally convinced the service manager to ignore complains from customers with oversize tires. Tire stores would gladly install the the tires , but not explain any of the down side of the added , un-sprung weight, and leverage against the brakes.
Problem was very apparent until Dodge increased the , rim size from 16" to 17" to accommodate larger rotors and calipers, that helped unless the owner went over 1 1/2" taller on the tires, then they faced the same issues.

Yes that's what I was thinking.
A 31" Tire would drop my rpms by 200.
The rear end change would do 300

I would rather do the rear end change.
The quote I got for gear changing is about $1450 complete. Then I would need a dealer or someone to recalibrate the computer.

Of course I'm going to contact a dealer Monday to ask for a quote on their rear end gear changes and if the are able to recalibrate the computer no matter who does it.

Thanks for replying all.

Any other mpg ideas or further discussion is welcome.

Thanks again.

[Hikerdogs]

First of all I doubt that you'll see any appreciable mileage difference changing the gear ratio from 4.56 to 4.10. You will however see a drastic difference in performance, and it won't get better. Secondly regardless of what Ford tells you the engine still needs a break in period. It doesn't have to be babied like engines of old, but the mileage will definitely increase as you get more miles on it.

Also keep in mind it's not exactly an empty box van. The chassis and house probably weigh well over 10,000 lbs. It also has the profile of driving a bill board into the wind. It's not aerodynamic by any stretch of the imagination. Driving a 13,000 lb. billboard into the wind at 60+ mph and getting 10 mpg doing it might be optimistic at best.

Our 2010 Ford (5.4 V8 and 3.73 rear end) truck got about 15 mpg for the first 10,000 miles. After we passed the 10,000 mile mark the mileage increased to an average of about 18 mpg. The same thing was true with our motorhome on the F53 chassis. It started out at a little over 6 mpg. Near the 10,000 mile mark the mileage increased to nearer to 8 mpg.

[CampDaven]

Any increase in MPG will not pay off the upgrade for a long time. Perhaps even a very long time.



Dave and Nola, RV Mutants

[sdagro]

Originally Posted by CampDaven

Any increase in MPG will not pay off the upgrade for a long time. Perhaps even a very long time.



Dave and Nola, RV Mutants

DITTO!! Several years ago I went from a 4.11 to a 3.73 on a gas burner and spent well over $1000. 12-14yrs later...if I still had truck I still don't think I would be fully recovered from the initial cost. Maybe 1.5mpg different....on a good day.

[JLC10756]

Ugg...
I now have 11k on the van. I don't see any mpg movement. So let's say the $1500 cost of gear change is 700 gallons of gas.
That's 4200 miles at 6mpg.
To break even figuring a .8 tenths of a mile per gallon increase ....
How many miles would I need to drive?
Like 12,000 more?

Again my math is fuzzy. So help is appreciated.

Also looking for easier driving. A little more space between shifts.

[twinboat]

One other consideration is the gear change itself.

They pull the axles, diff. carrier and then the ring and pinion.

It all sounds good, if the right guy does the job.

You may get the guy who doesn't have the experience and screws it up.

Now you have singing gears, oil leaks or a failed rear end, down the road.

[dix39]

Can you find information about the engine and what the most efficient rpms are to run it with the current loading? I think this would be somewhere in the area of where the torque/hp curves intersect, anybody?? If it were me I would nail the results down a little better than just guesses before spending the money.

Back in the early 80s I converted a '69 F 250 4x4 to diesel using a Perkins 6-354 engine. I found a ton of information in different locations that allowed me to calculate the most efficient cruising rpm for that engine would be. Then I researched until I found a way to arrange the gearing to allow the engine to run at that rpm while cruising. It worked out great and we hauled our camper all over the US with that old truck.

If you should choose to do similar research on your vehicle I think Ford would be a good place to start.

Best of luck.

Steve