gear change mileage help

thisfords4u · Dec 26, 2011

So if I change the gears in my wifes exploder from 3.73 to 3.27 for better mileage the tech calculater says instead of going 65 we'll now be going 74 mph so obviously we'll only go 65 mph so the rpms are going to be lower also. so what kind of mileage increase am I going to get. Its getting @20 mpg now. 91, 4.0 3.73ls, p235/75r15. Ulterior motive is the 3.73ls is going in the 87 trk. Thanks guys and Merry Christmas/Happy New Year.

snake · Dec 26, 2011

Probably won't gain a thing. It will be turning slower RPMs but it will have to work a little harder with the higher rear- which often offsets any gain.

doorgunner · Dec 27, 2011

snake said:
Probably won't gain a thing. It will be turning slower RPMs but it will have to work a little harder with the higher rear- which often offsets any gain.

on the other hand....it could get 2 mpg more--he didn't make a drastic change like I did (3.43 to 2.94)--which got me no improvement in city traffic/hopefully it'll make up the difference on the highway...

it's possible that he found the sweet spot..... :icon_thumby:

Explorin94 · Dec 27, 2011

You are getting 20 MPG with a 91 4.0 Ex? That's actually pretty good for it being about as aerodynamic as a brick. If it isn't broke don't fix it.

thisfords4u · Dec 27, 2011

well its 20 mpg hiway, we're 10miles from the hiway so theres alot of back road running around. plus my wifes one of those coupon gurus so once she gets to town theres alot of stop and go. So Im always hearing how its using so much gas. Ive got all the parts because I saved everything complete out of another ex., so its all just plug and play. I can swap everything over in less than a day.

Gotta_gofast · Dec 27, 2011

You might find a slight increase in fuel economy... but the money saved in fuel will most likely never equal or exceed the money invested in regearing your front and rear axles. Simply put, it'll cost you more to have the gears set up than you will save in fuel.

LearjetMinako · Dec 27, 2011

I would leave the gear ratio alone. 3.73 is a good ratio for mixed driving conditions. If you are solely a highway driver, then 3.27 would be okay. Probably a 3.55 would be better suited. Usually we change gear ratio for another reason, better gearing for the size of tire against engine power.

trail B2 · Dec 27, 2011

If you gain in mileage it will be highway not city but you don't drive highway much.Mama probably carries a bunch of stuff and Explorers are heavy gonna feel like she is dragging a trailer.Anything that breaks like the tranny u-joints for the next year it's because you changed those gears. Sounds to me like a trip from loving husband to the guy who f---ed up my car.IMHO

ZMan · Dec 27, 2011

You WILL see an increase. When my ranger had 3.08 gears I got 20+ mpg on the highway, when I switched to 3.73 it dropped to 18.5. I did a lot of highway driving with the truck back when I made the change, so it was pretty consistent.

You can change out the speedo gear to get the speedometer correct.

2manyfords · Dec 27, 2011

My brother had a "94 Explorer with 3.27 gears and it was slow and got crappy fuel mileage, barely over 20mpg Canadian gallons... Your 3.73 gears are much more driver friendly in a heavy Explorer.

LearjetMinako · Dec 27, 2011

trail B2 said:
Sounds to me like a trip from loving husband to the guy who f---ed up my car.IMHO

thisfords4u · Dec 27, 2011

Well like I said I have all the parts, complete front and rear axles and the speedo gear. But according to the calcs. you've given me it sounds like I'll only gain @1mpg. So other than entertainment swapping parts, I wont rush to get this done. Thanks for the input guys.

Original_Ranger84 · Dec 31, 2011

Yeah if you swapped the lower ratio you would get an increase in MPG's on the highway because once the vehicle is up to speed it requires very little power to maintain that speed unless its like really really fast so it shouldn't require any more power then the other gearing, you should see an increase becuase the engine is spinning slower to go the same speed.

The city driving will be affected alot though. with the higher gearing the engine will have to work harder to get the vehicle going, its pretty much the same as putting on larger tires there is more mass (or with gears less leverage?) for the engine to work with and ever stop and go will be harder.

If you do mostly city driving then 3.73 or 4.10's would be better, if you spend more time on the highway the 3.55 or the 3.27's. I'd say the ratio has to be 75% of your driving to make a difference though.

adsm08 · Dec 31, 2011

If it's mostly driven in stop and go traffic you'd be better to drop the ratio (numerically higher).

4.10s for city

3.73 for mix

3.45 and higher for highway.

doorgunner · Dec 31, 2011

you guys are correct about in-town ratios versus highway ratios....I learned that from my personal experiences (mistakes)...

as for us folks who want street vehicles with power.....and those folks who drive 4WD.....we are "hopelessly optimistic" about getting more than 1 or 2 mpg improvements....

dats a fak, Jack!!!!!

gear change mileage help

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