94 F350 4 DOOR 2WD DUALLIE 7.3 IDI TURBO E4OD 4.10: Looking for better mileage when running empty. I haul a big truck camper while towing a boat, 13K lbs total combined, so I don't want to change the 4.10 gears, I don't want to loose any pulling power. My highway mileage is 16-1/4 empty.

Thinking about installing a gear vendors overdrive. This would bring my RPM at 65mph from 2000 RPM now down to 1600 RPM with gear vendors overdrive. I would run this way unloaded only. My question is, will I save fuel by dropping 400 RPMs or will it be the same? Is this engine efficient at 1600 RPM?

 

First of all, 16.25 mpg is pretty darn good for the rig you got now. I only get about 15.5 - 16 on my F350 none turbo. One thing I have noticed is that the turbo is what gives you the most bang for your buck when it comes to milage increases as I am seeing on my 93 F250 which is turbocharged and gets almost 20mpg.

I myself have toyed with going with a GearVendor behind my E4OD on my 91 F350 to improve milage however there are two things that stopped me in my tracks.

1,0 Cost. The gear vendor conversion is expensive, even if I did all the work myself I was still looking at ~$4,000 to ~$4,500. Don't forget you need to shorten your driveshaft and re-align the angle on the rear axle to do this right.

2,0 The base E40D is not a very strong tranny to begin with and remember that HP thru the tranny is proportional to the product of RPM and Torque. Since you are going to be using the same Hp to drive as you are driving now, by lowering your RPM you are raising the torque the tranny sees which is going to be even harder on an already weak tranny. Your may have the perfect 2nd overdrive but end up with E4OD trouble. In all fairness you did state in your email that you were planning on running mostly empty (no towing or camper) so my main concern would be Cost. If you got the $$ go for it but be careful on what you expect in cost by future fuel savings.

Again I think a GearVendor would be great choice behind my 93 F250 with the manual ZF5. It would probably push its milage up to the mid 20's and the ZF5 with the DMF clutch can handle the extra Torque. Too bad the cost of the gearvendor installation is so high. I will have to keep my eyes out for a cheap used unit some day.

Lastly be careful, the Gearvendor has a minimum speed you must travel before it engages so don't put you hopes up that you will be doing much double overdrive during city driving. The benefit of the gearvendor really only comes in on the highway.



Sebastian.

 

Unless you do a lot of highway miles it will take years to save the cost of the overdrive.

Using 3.50 a gallon for fuel cost and driving 10,000 miles,
at 15 MPG you spend 2333.33 for fuel.
at 20 MPG you spend 1750.00 for fuel.

583.33 savings for 10,000 miles

So you will break even in about 45,000 miles if you do the install yourself.

On the plus side, fuel will increase in price so it will pay off sooner.
On the down side, you have a vehicle that is as aerodynamic as a cinder block.
It is heavy and has a large frontal area.
There will be a point that the MPG will stop increasing no matter what you do.
I can't tell you where that point is, there are to many variables.

 

just along these lines of thought, can a gear vendor overdrive be installed on a 4X4? not intending to sink that kind of $$$ in a rig, just wondering if it could be done realistically.

speedrdr

 

16 MPG is very good for a truck like that. 1600 RPM is doable, but dont even think about towing at those revs. My truck turns 1600 at 70 MPH, and its only good for running empty or a very light load. A stock E4OD may tend to overheat running such low revs because the oil pump turns at the same speed as the engine. My expereince is that 2000 RPM is the best overall compramise engine speed for combined driving conditions on the highway.

It is possible to save SOME fuel like this, but as soon as you hit a head wind or hill you will loose any advantage that you had because you are running the truck below the peak torque range.

the way I have mine set up, overdrive is basically used as you propose to use the GV overdrive. At 65 MPH, its turning at ~2000 in 3rd gear (with TC locked), at the same speed in OD, the RPM is just below 1500, not really usable, and generally I will see the same MPG running in 3rd as in 4th at 65 MPH.

Now having said that, I live in BC, and there is not much flat ground on the highway that I drive, if I lived in alberta, than it might be different. My point being, if you spend a lot of time on flat, open road, than you could gain a little, but 20 MPG is always a tough goal, I don't see that very often. Your situation may be different.

 

Yes Gear Vendors has an overdrive for the 1345 and 1356 transfer cases.
Several others as well, but I remember those because they are the most common in our trucks.
It replaces the back cover of the transfer case.

 

The GV installs on 4X4 jsut fine. But it is electronically locked out, as soon as 4WD is engauged.

Because it only effects the rear axle. If it engauged while in 4WD, the gearing differance between the front and the overdriven rear, would evantually detstroy one of the R&P's

 

My 94 7.3 IDI Turbo 4X4 came with a GV already on it. I use is everyday but also I commute 35 miles each way on the highway. I believe it kicks on once the truck hits 35 or 37 mph. I probably would not by one if I did not have one already due to the price. I will definately remove it and reinstall on a newer truck if I sold my current truck. 3K is an alfull amout of money though.

unloaded about 18-20 MPG
Loaded 13-15 MPG

4.10 gears w/ 35" tires.
E4OD