engine speed for best fuel economy?

[LCAM-01XA]

In high gear where do you guys like to keep your IDIs for lowest fuel consumption, what RPMs? When I was picking up my truck the guy told me it gets best economy at about 2000rpms, but I've ran it at 1800, 2000, and 2200rpms on the cruise and it don't really seem to make much difference... Engine is stock, with just opened up intake and a straight-piped exhaust and the injection pump turned slightly up. So yeah, post your observations

 

[Shadetreemechanic]

If I can keep mine below 2k on the highway I generally get 22mpg. It drops off pretty quickly if I cruise above 2k. With your 4.10s you will be still going pretty slow at that rpm

 

[allczns]

wind resistance?

how does wind resistance factor into this? If wind resistance is x at 40 mph, is it 8x at 80 mph? And how significant is that with respect to mileage?
I've read that the torque peak is ~ 1600 rpm for our engines. Is that the optimum rpm for best mileage?
just wondering,

 

[FordGuy100]

Yeah, I would say right around 1600rpm's in your tallest gear would be the best for fuel economy. Wind resistance is almost a squared thing if I remember right, so at 40mph your at X^1, but at 50mph your at X^2, I'm probably wrong though.

 

[dakotajeep]

Wind resistance is almost a squared thing if I remember right, so at 40mph your at X^1, but at 50mph your at X^2, I'm probably wrong though.

Your actually 100% correct....

 

[LCAM-01XA]

If I can keep mine below 2k on the highway I generally get 22mpg. It drops off pretty quickly if I cruise above 2k. With your 4.10s you will be still going pretty slow at that rpm

You get 22mpg? Damn! Does your truck have a turbo? And yes, you're right on the low vehicle speed, at 2k I'm only going 60mph, but that's usually what the 18-wheelers move at too, so I just line up with them and hit the cruise. The slowest I usually roll the freeway without the fear of being run over is like 55mph, which is about 1800 rpms, next time I'm doing a night drive I'll just keep it at 1600rpm (around 50mph I think) and see how much that will get me.

As for wind resistance, that's correct, it gets exponentially worse as the speed increases. Also the more air you got flowing under your truck the more resistance, thanks to the axles and tanks and all that good stuff, hence why I got that big aluminum sheet under my bumper - without it ground clearance is over a foot, with it much better for street driving.

 

[Shadetreemechanic]

You get 22mpg? Damn! Does your truck have a turbo? And yes, you're right on the low vehicle speed, at 2k I'm only going 60mph, but that's usually what the 18-wheelers move at too, so I just line up with them and hit the cruise. The slowest I usually roll the freeway without the fear of being run over is like 55mph, which is about 1800 rpms, next time I'm doing a night drive I'll just keep it at 1600rpm (around 50mph I think) and see how much that will get me.

As for wind resistance, that's correct, it gets exponentially worse as the speed increases. Also the more air you got flowing under your truck the more resistance, thanks to the axles and tanks and all that good stuff, hence why I got that big aluminum sheet under my bumper - without it ground clearance is over a foot, with it much better for street driving.

Factory turbo, EO automatic, 3.55 gears, and 265 tires. It has also been said that I drive like I have an egg under the gas pedal, but on highway I manage 22 pretty consistently, with 18 mixed driving. I run between 14 and 16 towing my 7k tractor, but then I almost never exceed 65.

 

[RKOCH]

Mine runs best @ 3000 @ 70 mph with 4.10 gears and 38.5 inch tires. I have no clue about milage I just fill it up when empty.

 

[Mike]

Mine runs best @ 3000 @ 70 mph with 4.10 gears and 38.5 inch tires. I have no clue about milage I just fill it up when empty.

 

[4x4TruckinGirl]

I'm gunna be able to do a good test run with my truck next weekend, I'm headed to Miami..... i'll post up then what I'm runnin'.......

 

[MUDKICKR]

4x4TruckinGirl how does your trk look with 7" lift and 35's? my 92 f350 has 5" lift and 37's and i think the 37's still look a little small. but i have 2" add-a-leafs, 3" body lift and cut out fender flares. my trk sits 2" higher in the rear but not for long

 

[4x4TruckinGirl]

I'm gunna post some pics later of the truck...... hehehe, i just got it out of the paint shop sooooooo..... you will be able to see the lift and stuff too........ I just need to go out and take the pics, lol......

 

[Diesel JD]

Might be a good test run. That traffic can get pretty dense on the turnpike. I took my truck down to Coral Springs from here a couple times in 2005 and wound up getting around 14mpg but that was with the 4.10s 3000rpm at 68mph and before I started using B100, truckstop diesel from Petro there in Ocala back when it was only $1.99/gal the good old days.

 

[4x4TruckinGirl]

I'm not 100% sure what gears are in my truck...... today i was really thinking about it... i was at 65mph and about 1700/1800 rpm..... whats ya'lls guess?

 

[Diesel JD]

4.10s or lower with those oversized tires and ZF trans. Here's a calculator if you want to play with the numbers a bit http://ringpinion.com You just need your tire height gear ratio and rpm. Logic dictates you could use algebra to solve for the gear ratio value but since I hate math I'd just plug different known gear ratios in to the calculator and see which matches best. I'm thinking its gotta be 4.10s or 4.56 since you have those huge tires 37" right?