1995 F150 XLT Supercab 4x4 Shortbed
351w 190,000 miles
E4OD trans with OD
4.56 gears
33"x12.5 GoodYear Duratracs @ 30 psi (max is 35)
Leveling kit plus 3" body lift
Regular grade gas
Semi Synthetic 5w30 high mileage oil

Normally get 12-13 mpg city

Took a Trip on the interstate...completely empty load.
30 mph crosswind, 80 deg F
75 mph for 400 miles and got 9 mpg.
65 mph coming back and avg 11 mpg with no wind.

60 mph = 2000 rpm
65 mph = 2200 rpm
70 mph = 2400 rpm
75 mph = 2600 rpm
80 mph = 2800 rpm

That's with OD. If I drop to D @ 60 mph the rpm is 3000, so thankfully OD nets me 1000 rpm @ 60 mph.

What is the recommended best fuel economy speed/rpm for my engine and configuration...55?

What has the biggest impact on my mileage...the tires, gears or lift in what order? I really didn't think it'd be that much worse than city miles that are stop and go and hills here in Colorado. All the highway driving was flat on I-70.

 

Well them 4.56 gears are not for mileage, I would think that at 75 mph, you got pretty good mileage, 55 mph is going to probably give you about the best you can expect with that truck, in my experience.

Trucks and good fuel mileage in the years we normally discuss on here, do not belong in the same sentence, large trucks are not conducive to good fuel mileage.

 

youre lucky to get 12-13 city, IMHO. In my ecperience, going over 65 drastically lowers mpg. with 4.56 gears 55 sounds right to me as well.

 

those 4.56 gears are not good for highway driving. 55mph sounds about right with that kind of gearing. Honestly, I would be more than happy with your kind of milage at 65-70mph. I have a 92 f150 SCLB 4x4 with 351w, e4od trans, stock 3.55 gears, 3'' body lift, and 35x12.5 xterrains, and I am lucky if i get 8-9 at 60mph

 

Did you recalibrate the speedo for the larger tires?

 

Yes I did recalibrate and it's right on. What is the biggest factor on the low mpg...the lift, big wide tires, my gears...I know they all three do together but was considering 4.10 or 3.73 gears since I don't off road much anymore. My next job will require about 2 hours of highway time per day. I don't want a Prius! I love this truck.

 

The lift and wide profile tires are the biggest reason your highway milage sucks, if it was gears your city milage would also suck just like OldBlack4x4's truck does. Proof is that your city milage is still about exactly the same as stock and because 2000rpm at 65mph is essentially the same as what you would get with stock tires and 3.55 gears. Some narrow profile(8") tires with a non-aggressive tread but same height would help, if you can hear the tires at highway speed they're too aggressive. With no wind your truck should cruise at that speed with very light throttle, make sure the hubs are disengaging properly so there is no more drag than necessary.

 

I'm lucky if I get to 65 miles an hour much less over 5 mpg. My truck is also a crew cab long bed 4x4 f350 with a 351W that has 4 shot rings and an e4od on 36x14.5s(no lift).

 

Not disagreeing about lift, tire width and tread being big, but I wouldn't rule out gears hurting the highway mileage. A 33" OD tire with 4.56 gears is the same as a 235-75R15 tire (29" OD) with 4.00 gears. So you are running your engine faster than stock tires with 3.55 gears. And the low gears will hurt your highway mileage a lot more than your city mileage since it's only on the highway that those gears will put your engine that fast. In fact, the low gears probably actually help your city mileage as they make it easier to get a big truck moving.

If you are only worried about highway mileage I'd look at the gearing a lot harder. But if you don't want to lose city mileage I'd go with what Conanski said. Narrow highway tread tires will help you all around. And even for highway-only, it'll be a much less expensive route so it''l probably give you the most bang for your buck.

 

I don't totally disagree but the gearing would have to produce excessive engine rpms to have a significant impact on highway fuel milage and 2000rpm at 65mph is far from excessive. When I had my tuner connected on my truck it would show the instantaneous fuel milage as you drove around, in OD at 50mph my truck only turns about 1500rpm(3.55 gears 30" tires) and the tuner indicated about 12mpg, shift to Drive and rpms jump to about 2000rpm and fuel milage also jumped to high teens. Speed up with the trans still in D and milage goes down again the faster you go, this is a result of engine load which with an EFI motor is the major determining factor in how much fuel is used. So lowering engine rpms is not always better it's more of a balancing act, too much gear is just as bad as too little, but aerodynamics also plays a major role at highway speeds so the taller the truck the worse it'll be and there's not much you can do about it besides lower it or drive something else on the highway.

All that said from what I have seen 1800-2000rpm seems to be the sweet spot for fuel milage with these 5.0 and 5.8 trucks, whatever speed you can achieve with the trans in top gear will produce the best highway milage.

 

12-13 is what my dad's stock 96 351w gets. Consider yourself lucky.

 

I think he should feel lucky about his 12-13 mpg city. But not his 9-11 highway. My '95 F-150 was pretty similar and it got 12-13 highway (the same 4x4 SuperCab short box, 351, E4OD and 3" lift, but mine had skinny 33-9.50-15 all terrains and 3.55 gears).

 

I can manage 14 with my truck on the highway at 80 mph. I did a tank at 55 as well with the OD locked out and got low 15's out of it.

 

Your RPMs & Speed can't be right with 4:56 gears. My Dodge V10 5 speed with 3:55s turns 2100 RPM in 5th gear OD @ 70 MPH. With 4:56s you should be turning up in the 2600+ area @ 70.
As for mileage your doing great if you truly have 4:56s gears with big tires.

 

Those numbers seem almost dead on according to this calculator that I use all the time.

Engine RPM Calculator

Keep in mind the E4OD has a deep overdrive of .71. I turn ~2200 rpm at 80 mph in my truck in overdrive.