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Old 01-30-2012, 08:43 PM   #1
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Default 3.31 or 3.55 rear end

Test drove a 2012 EB SCREW 4X4 today with the 3.55 rear end.Thinking about a purchase in the near future and was curious if there is going to be much difference in the fuel mileage between the 3.31,3.55 and 3.73 rear?I will only be towing my ATV trailer. Salesman said there would be very little difference between them. I am looking for the best hwy fuel mileage possible..Thx.
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Old 01-30-2012, 09:45 PM   #2
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Quote:
Originally Posted by SSG665 View Post
Test drove a 2012 EB SCREW 4X4 today with the 3.55 rear end.Thinking about a purchase in the near future and was curious if there is going to be much difference in the fuel mileage between the 3.31,3.55 and 3.73 rear?I will only be towing my ATV trailer. Salesman said there would be very little difference between them. I am looking for the best hwy fuel mileage possible..Thx.
The salesman was right for a change that there is not a very big difference between them unloaded. Due to the amount of low end torque it has, the EB is not as affected with gear ratios as most other gas engines. This is all to preference really. If you were going to get plus 2 or bigger tires then I would say go with the 3.73. If you are gonna stay with the stock tire size or a plus 1 then a 3.55 will do just fine. Being that it is going to be a 4x4 then I would stay away from the 3.31 but that is just me. I am sure that the 3.31 will tow the amount of weight you need to with no problems, but I kinda see having a 4x4 kinda defeats the purpose of wanting to save gas with a 3.31 ratio. Besides, the money saved in fuel would probably only buy you a gallon or two worth of gas annually since there is really no big difference in MPG with the different rear ends on the EB.

Edit: Sorry, I didn't fully read you post. If you are looking for best hiway fuel milage then I woild go with the 3.7L. It will easily tow atv's and give you better MPGs then the ECO plus it costs less.

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Old 01-30-2012, 10:10 PM   #3
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Thanks for the info...
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Old 01-30-2012, 10:30 PM   #4
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I agree with Al Kohalic in that the ample torque available in the EB allows the taller 3.31, 3.55 gears to be quite effective in towing moderate loads. I have a 5.0 with 3.55's and it does just fine. So an EB with 3.31's should also be fine for the odd recreational heavy tow/load.

As far as the best for mileage. IMO, the 3.31. Trolling through the EB mileage threads (and there is a lot of them), many of the guys complaining of poor mileage have the 3.73's (and many with oversized tires, so gearing may not have as much impact). Seems like it shouldn't make a big difference, and in many instances it doesn't. But if you're a prospective buyer who honestly is using your truck for commuting more than towing/hauling, I would recommend the 3.31's. If you're pulling all the time, you're not going to go wrong with the 3.73's. The 3.55's are very capable and are there for those of us that want the compromise gear, cause we can't decide one way or the other.

There was an EB thread which also discussed how well the 3.15's pulled.

Lots of choices, but if you consider your needs well, you'll choose the right one.
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Old 01-30-2012, 11:27 PM   #5
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3.31's are the standard SCREW 4X4 ratio, but it is an open rear end...no limited slip or electronic locking option. I would get the 3.55's to get an electronic locking rear end.
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Old 01-31-2012, 12:03 AM   #6
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There isn't enough difference between the two to matter MPG wise. You could go from 3.31 to 3.73 and still only maybe see about a 1 mpg difference. You have to have a pretty drastic change in gear ratios, maybe from the 3.15 to the 3.73 before you'd start having a really adverse effect on highway mileage.

Ford offers (and probably builds a lot of) the 3.15 and 3.31 configurations for CAFE, where .25-.5 mpg across one hundred thousand vehicles significantly affects their corporate average. Half a mile to the gallon to the average driver would require a couple years worth of driving to amount to much of a difference to your wallet.
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Old 01-31-2012, 01:30 AM   #7
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I don't think the gears make that much of a difference. If you never get on the throttle and one atv is all you will tow then I'd agree that the 3.7 is the best for you(which has a 3.73 gear but still gets the best mileage of any f-150). If you like knowing the power is there but never use it and want the ecoboost for that then get the 3.31. If you are buying the ecoboost because you love torque and power get the 3.73. If you're in the middle then the obvious choice is the 3.55.

On a side note, the 3.7 can be had on the screw but not with 4x4. The supercab with 4x4 can be had with the 3.7 though.
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Old 01-31-2012, 02:12 AM   #8
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Get the 3.31. You'll get better mpg at a higher cruise speed and the engine is plenty torquey. The key is to keep the turbos spooling as slowly as possible for best mpg.
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Old 01-31-2012, 10:22 AM   #9
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I'll agree with the others - for your purposes, get the 3.7L. If you want *decent* gas mileage and still have plenty of power in reserve, get the EB.

I wanted a Lariat, and I honestly use my truck to commute in (probably 90% of my driving is commuting), so I got the EB with 3.55 LSD (don't need a locker, wanted LSD).

Now that I have my truck, I've hauled firewood, furniture and other detritus, and the EB has done it all without even having to breathe heavy! My MPGs are about dead on with the EPA ratings (15/21 city/hwy) now that I've got 4,000 miles on her and the engine is somewhat broken in.

Just my $.02 - hope it helps!

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Old 01-31-2012, 01:37 PM   #10
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Originally Posted by EricTheOracle View Post
Get the 3.31. You'll get better mpg at a higher cruise speed and the engine is plenty torquey. The key is to keep the turbos spooling as slowly as possible for best mpg.
At cruise, the turbos will only produce a negligible amount of boost regardless of gear ratio. Boost is not only dependent upon RPM, but throttle opening and engine load. You can run a turbocharged engine with no load at 5000 rpm and produce very little boost.
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Old 01-31-2012, 01:37 PM
 
 
 
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