Advice on Final Drive Ratios

Skeletor

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Hey everyone. I was hoping maybe some of you all could offer some guidance for me as I'm a little stuck on which way to go.

I plan on buying a Big Bend 4dr with the 2.7 auto. This car will be my DD and family hauler, mall crawler etc. I don't really plan to do much rock crawling, but I might take it down some rough roads on occasion to go camping, fishing. Also, being able to get around in snow is a must. I plan to stick with the standard 32's on the BB. I might bump up to 33's, but I doubt I will ever go larger than that.

I also drive approximately 60 miles, round trip, to and from work daily. I'm trying to decide between the 3.73 open axle and the 4.27 with the locking differential.

MPG is definitely something I'm interested in maximizing as much as possible. (Yes, I understand this thing is not going to be great on gas.)

Can anyone offer me some advice or insight as to which way I should go? Thank you all in advance!





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Skeletor

Skeletor

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Thank you for the reply. I read through those threads and they are definitely informative for sure.

I guess I'm left with a couple final questions. I guess I'm wondering how much will the jump to a lower ration really affect the gas mileage? 3.73 is probably going to maximize the gas mileage, but would move to the 4.27 make that much of an impact?

I guess also, given my circumstance and intended uses, would the detriment to the gas mileage out weigh the benefit of the rear locker?
 

The Pope

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The move to the Lower Gear (4.27:1) wouldn't cause much of a MPG difference. If I had to guess........0.2 to 0.5 MPG difference, but that's a total guess...

But going with the 4.27:1would get you the Lockers, which, in my opinion would be better to have and not need vs. not having and needing.
 

Drex

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14% faster engine speeds per MPH, steady state commuting... I estimate a 1-2 MPG hit for the steeper gears. If you ever need gearing advantage off road, well... You have a low range, so I don't see a need to spend an extra $800 (plus tax and financing on that amount) if it is going to be a commuter for almost all is usage with iffy fishing roads occasionally. Spending the money from fuel saved and option saved money on good tires is probably a better trade-off then gears and a locker as per your intended use. Having said that; if you are serious about increasing tire size (another MPG hit), get the gears and the locker. I would imagine you'll get the cost and maybe more, back when you sell it over an open rear end.
 

JT1

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Thank you for the reply. I read through those threads and they are definitely informative for sure.

I guess I'm left with a couple final questions. I guess I'm wondering how much will the jump to a lower ration really affect the gas mileage? 3.73 is probably going to maximize the gas mileage, but would move to the 4.27 make that much of an impact?

I guess also, given my circumstance and intended uses, would the detriment to the gas mileage out weigh the benefit of the rear locker?
Having driven in WV, spring for the lockers and gears, you might actually get better mileage. Less downshifting up hill and the ability to stay in higher gears without lugging the engine..
 

TrailDust

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I've always gone with the deepest gear I can get, you never know what you might do and you always regret it when you didn't get them.

Sometimes mileage can be funny too. Swapped 3.73's out from my old 2007 F-150 when I blew them up with 4.10's when the 3.73's were backordered. Ended up gaining about 2 mpg with no other changes, think the 5.4 was in a better power band.
 

Used2jeep

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The 10 speed, IIRC, also has 3 different "better than direct drive" gears (.9, .7, .6 ish) so that should help out your MPG concerns.
 

Markubis

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The 10 speed, IIRC, also has 3 different "better than direct drive" gears (.9, .7, .6 ish) so that should help out your MPG concerns.
Correct, the top 3 gears are "overdrive" gears and less than 1 to 1
 

LarryZiegler

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Correct, the top 3 gears are "overdrive" gears and less than 1 to 1
Agreed, but I am open to rebuttal on this: in the old days when we had a 3 sp auto with a 1.00 3rd gear ratio, today we have a 10 sp auto with a .636 overdrive, thus turning a 3.73 gear ratio to a 2.37 final gear ratio. I’m thinking on my OBX trim order of going to the optional 4.27 gear ratio with the stock 32in tires giving me a 2.72 final gear ratio. In my memory is my 1970 Ford Bronco with a 3.50 axle ratio, 30in tire/wheel upgrade and a 120 hp 302 V8. Top speed was 75 mph and it took adding a set of headers and dual exhaust to bring performance back to its stock tire/wheel (G78-15 or 215/78-15 equiv size) performance level. The big difference is a 310hp V6 to push this 4500 lb vehicle down the road (the original Bronco weighed approx 3500 lbs)
That’s my reasoning to opt for the 4.27 gears and I’ll accept opinions if I’m wrong in my assumptions
 
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Drex

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Sometimes mileage can be funny too. Swapped 3.73's out from my old 2007 F-150 when I blew them up with 4.10's when the 3.73's were backordered. Ended up gaining about 2 mpg with no other changes, think the 5.4 was in a better power band.

Theoretically possible, the engine might have been in a more efficient RPM/load range. I am curious though, you increased the odometer/speedometer readings by right at 10% with that gear change. Did you adjust via speedo gear or programming so that your odometer was accurate? If not, reduce the total MPG by 10%, which was probably darn close to 2MPG.
Edit; unless it used a reluctor tutor system for this functions. Was your speedometer reading 10% high?
 
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TrailDust

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Theoretically possible, the engine might have been in a more efficient RPM/load range. I am curious though, you increased the odometer/speedometer readings by right at 10% with that gear change. Did you adjust via speedo gear or programming so that your odometer was accurate? If not, reduce the total MPG by 10%, which was probably darn close to 2MPG.
Edit; unless it used a reluctor tutor system for this functions. Was your speedometer reading 10% high?
I installed an Edge Evolution in it at the same time so I could program the ratio change. I didn't put a tune into it at first because I was curious about the gears affecting the MPG. I did end up running it on a tow tune most of the time after and it got significantly worse MPG, mainly due to my right foot because it was so much more fun to hammer on.
 

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