Do you think your speedometer is accurate?
All the tire sizes I have are for mud tires, a 235/85-16 tire is 31" tall.
With a 31" tall tire and 4.10 gears and a A4OD in OD you should be running 69.7 MPH at 2200 RPM.

1900 RPM should be 60.2 MPH.

 

Just for a quick comparison.....

355LS axle.....235/85/R16 tires........E4OD in OD

60mph....1650 rpm
70mph....1800 rpm
80mph....2100 rpm

 

mines a 1985 Ford 1 ton crew cab dually with only 172 k miles on it , 6.9 diesel, 4 spd manual, i feel up when between a 1/4 tank and empty but my back diesel guage always goes a 1/4 below empty before its actually empty too and the front tank dont know havent found out completely jsut know it kind of like the back tank. i dont have a tach but would like to know how to hook one up and mine has 3:73 gears in it and running 235/85R/16 on the back and 265/75R/16 on the front but the back tank i get only about 200 or alittle more out miles out of it, and front tank i can go about 300 or more but the back tank on mine is only 15 gallons my old pickup was only 14 gallon for the back tank on a 3/4 ton pickup , mine has an auxilary fuel filter under the hood which im going to take out and i change them regularly and oil change every 3k miles too, has dual exhaust but one muffler which i dont like though, it runs good but have to have power supply fuel treatment or marvel mystery oil or berryman diesel octane boost in it to get any mileage out of it everything is stock other wise i have a K&N Filter in it for now what are the other choices to get alittle better mileage than about 12 or 13 out of the back tank and i do run the speed limit most times but even when i do and when i drive 85 or so the mileage is the same for the back tank jsut wondering why it does this any help would be nice and dave i apologize about the turbo thing i didnt know ATS turbo kit box looked like that never can get a reply from them about my pickup or arrowcraft about alcoa wheels either or banks for that matter for exhaust so any help would be greatly appreciated from any and all. thanks Lance

 

Here are my indicated speed/rpm/mph figures. My truck is a 1994 F-250 IDI TD, 4.10 gears, E4OD trans, 4x4, extended cab with a cap on the back. 235/85/16 tires (BFG commercial, not mud tires). I suspect the reason my figures are different than Dave's is because mine are indicated, not calculated (i.e. the tach and spedo may not be all that accurate) and I have regular street tires which are probably a bit shorter than mud tires due to the lesser tread depth.

Cruise Control set at 70mph (about 2250rpm) --> 13mpg

Cruise Control set at 60mph (about 2000rpm) --> 16.5mpg

Cruise Control set at 55mph (about 1800rpm) --> 21.3mpg

 

man i must be doing something wrong, i cant get close to those figures. here are mine i will take any sugestions.
mph tach gas
65 2300/2350 14.6
70 2450/2500 14.3
75 2550/2600 13.8
i have a banks sidewinder kit 92 350 4.10 and a zf5 tires are 235/85/16, i dont know anything lower than 65 because i would get run over down here. the truck is almost never loaded anymore other than a 100 gallon fuel cell in the bed that stays full. it costs to much to drain it and fill it all the way up again

 

I dont know, is the gear raito of the ZF5 the same as the E4OD? It looks like your mileage figures are about right for the speed you drive (actually a bit better), but it looks like you are turning a bit more rpm than I am.

 

all of my figures were actual figures from the dash. i didnt calculate them so they may be a bit off. also i use a diesel additive called diesel kleen, but i havent seen any difference in the mileage. dad had a 2000 power stroke 350 and it got him about 2 miles better. i am still testing to see if it will help me.

 

The A4OD has an overdrive ratio of .71
Low gear is 2.71 in the A4OD

The ZF 5 has three different gear sets that could be in it.
The overdrive is either .77 or .76 in all the sets.
Low gear is where the most difference in them is, either 4.14, 5.08 or 5.79

 

Theres my problem, I have to keep it under 80 mph. I live in the central valley of CA. and 80 mph is just keeping up with traffic. 91 F-350 crew cab dually, w/93 7.3, banks sidewinder, us gear od., 4.10 gears. 100 gal. transfer flow aux tank, 10-12mpg without fifth whee trailer.

 

does anyone know what the 6th gear is in the 6 speeds in the new powerstrokes. and or know of anyone that has done this swap,

 

Last night I got on the Highway and ran a test on the tach:

60 MPH @ 1800 rpm
65 MPH @ 1925 rpm
70 MPH @ 2025-2050 rpm


It sounds as if the speed could be the issue here for such low MPG. For that matter when should new injectors and or pump be installed?
Thanks for the help

 

Why165, the six speed tranny has an overdrive of .72 and will bolt to the IDI motor.
But if you have a 4x4 you must also change the transfer case.

That is a great transmission though, I am saving my pennies till I can afford one with the new transfer case as well.

 

scrv1977,
1740 = 55
1900 = 60
2050 = 65
2200 = 70
2370 = 75
2530 = 80
Assuming your tires are close to 31" tall you should see these RPM's at these speeds.
If you know where to find a measured mile and hold the speedometer on exactly 60 MPH for the mile, you should drive it in exactly 60 seconds.

I do this to check my odometer and speedometer regularly.
There is a 10 mile stretch of measured miles about 20 miles down the interstate from my house.
This way I know I am using good numbers for my mileage calculations, and I also know that if my speedometer says 65 MPH, I am going 65 MPH.

My truck came with 235/85-16 all season tires, but when I had them on it and was running 10 MPH over the speed limit everyone was passing me.
Then I found out my speedometer was way fast. (10 MPH )
285/75-16 mud tires put it right on the money, but I lost several miles to the gallon when I figured the mileage. Part of the reason was the bigger tires and rough tread dropped the mileage some, but I also actually went as far as the odometer said I did.

 

who does a swap like that and about what does it cost?? everyone i call says it cant be done or never gets back to me with any information. if it will bolt right up what about the splines on the output shaft on the motor??
92 350 banks sidewinder 4.10 zf5 cc dually

 

Let me talk to my driveline guy sometime this coming week, he said I could put one in my 86 but I had to buy a new transfer case to do it since I have a 4x4 truck. I know that the transmission is about 3000 dollars new and there are none in the local salvage yards yet.
The input shaft is not the problem, it only goes into the clutch disk, the problem is the output shaft. On a 2 wheel drive you would only have to get the right yoke for your driveshaft u joint size. Several are available.

On a 4x4 you must have either a NP 271 or NP 273 transfer case that came on 99 or newer trucks.