3.27 overdrive and gas mileage

[Flandry]

Acceleration is what eats most fuel, and the higher ratios do that more efficiently. Once at speed cruising, the lowest gear ratios will produce the best fuel mileage...The key is to select the ratios that best match your vehicle usage. If you can say that you rarely slow down for hills, traffic, lights etc, then lower ratios will be best for that. It's a compromise, we have discovered along with Ford during the 90's that the 3.73's are about the best for typical driving. If you drove hundreds of miles at a time on flat highways, rarely in cities, then you need 3.55's or 3.27's.

Thanks for passing on the info. My personal observations have indicated this, so it's good to hear someone else saying it too. Like any red-blooded American, I like acceleration and I like speed. So adjusting my driving to optimize this axle has really taken some doing.

The best fuel mileage should come in the very bottom of the torque peak, not at the peak. I believe that that rpm is in the low 2000 range, 1700 may be a hair low.

Interesting. My Ex seems to, for lack of a better description, drive easiest at about 1900 RPM. For the terrain I drive, this usually puts me in the 55-60 mph range. Maybe this is the bottom of the torque peak for me.

 

[CDW6212R]

That's a big reason that I think that I may gain something by swapping gears. My 99 truck seems to run a couple of hundred rpm's higher than I'd like most of the time. This truck has been next to my V8 in terms of my worst mileage vehicle. With 4.10's that is my worry. I just swapped my 3.73 out of my 98 truck, so now I have a pair of 3.73 diff's to work with.

 

[Four0Sport]

to throw in my 2 cents.. alot of 'fuel economy' ratings and personal results will differ between our vehicles depending on where we live and how we drive. you guys out there getting 18, 20+ mpg, i envy you. my 4.0L averages 12-14 mpg while my 5.0L averages 15-17 mpg. I am not constantly on throttle, my vehicles are in good running condition and regular maintenance is performed but i live in WV. my 25 mile trip to work is nothing but interstate with hill after hill after hill to climb. the v8 doesnt have to work as hard to climb hills which is what i mostly contribute to the better mpg, and the 3.73 rear end. my 4.0L has 3.27 open diffs and combined with the lower hp and torque, has to work harder climbing mile long mountains.

epa fuel economy estimates are exactly that, estimates. im sure that if there was 0 wind and i was driving on miles of straight blacktop in OD at 55mph i would get 20+ mpg, but the fact is that i drive against the wind up hills in a vehicle as aerodynamic as a cinder block.

 

[Flandry]

to throw in my 2 cents.. alot of 'fuel economy' ratings and personal results will differ between our vehicles depending on where we live and how we drive...

I absolutely agree with you. All I need is one commute drive in heavier-than-normal traffic to watch my fuel economy for the whole tank drop by 2/3 to 3/4 mpg on average.

epa fuel economy estimates are exactly that, estimates. im sure that if there was 0 wind and i was driving on miles of straight blacktop in OD at 55mph i would get 20+ mpg, but the fact is that i drive against the wind up hills in a vehicle as aerodynamic as a cinder block.

EPA ratings are nowhere near real-world. However, in defense of the venerable OHV-in-a-brick, it's not quite that bad. I drive a combination of highway and city miles with wind (I'm in Tornado Alley) and terrain that, while not as bad as yours, is still the southern tip of the same mountain range. I also never drive as slow as 55 on the highway. Yet I'm still able to top 20 mpg with a straight-stock setup.