So...a question that has'nt really been answered or maybe in a different form...Has anyone really noticed or done much math on the MPG difference between the 3.31 "Non Limited Slip" vs the 3.55 "Electronic Locking axle"?

1mpg isn't to bad but 2+ seems to be pushing it IMO.

Thoughts?

 

How many of you Ecoboost owners have the 3.31 and how many went with the 3.55 and for what reason?

Thanks

 

IMO the reason to get the 3.55 gearing would be someone that does occasional towing with something that is not very heavy. (up to 5,000 lbs.) The person getting the truck that will not tow with it would benefit from the 3.31 gearing especially in milage.

That's the way I see it.

 

Fair enough,

The problem I'm having is the 3.31 is only offered as a non limited slip axle, for the locking axle I'd have to get a 3.55.

Everyone states the mileage difference is very minimal maybe 5 or so per tank but others keep saying the non tower will benefit from the mileage of the 3.31 so It's confusing. As for the locking rear, Iowa has some drifty roads, I have no plans of off roading or pulling anything really maybe some very minor off roading at the most so I'm not wanting to get stuck with the non limited slip if i get in a jam, even if It's 4x4.
Thoughts?

 

I think you're over analyzing this, bud. You already know what you want. Get the locker. You'll simply regret not having the locker and you know that to be true.

 

If you want the locker, get it. It is worth the extra $400. If you are so set on getting 0.5 more MPG, get the 3.31 and you will be able to use 4A all the time if you need to.

 

Where the milage will be more than .5...I do agree there is not a huge difference between the two. I was merely telling him the differences of why I would chose a higher gear ratio.

I am not really sold on locker or LS as of yet...however the ones I have been looking at have all been E-lock.

 

Due to tow capacity, I went with 3.55. My options were actually the 3.55 LS or the 3.73 E locker. I pulled my RV with both and could not tell any real difference while towing. I did notice about 100 rpm difference at highway speed between the 2 gear sets.

I got the 3.55 because that truck had some of the things I wanted inside. PLUS it was a 2011 used and was priced a good 7,000 cheaper than the 2012 out the door.

 

I sometimes use the 4a function on mine in really hard rain or at the beach and I love it. It engages so quickly and quietly you forget about it. I was using it one day in the rain and got caught at a train so I went to spin the truck around from a stop thinking it was in 2wd and the 4a instantly kicked in and turned me right around without spinning a tire. It kinda acts like an AWD but without robbing the fuel mileage.

 

Can you help me out with the math? I actually consider the 3.55 to be the best overall gear choice with the ecoboost engine but it's gonna be pretty hard to compare MPG's when we all drive differently and most of us are in different parts of the country.

Most of you assume the 3.31 is a waste of time. Well, it is if you're looking specifically for an LSD or an E-locker. I assure everyone here that the 3.31 and the EB will whip this truck around like a wet dish towel.

Most of us have seen the GM videos that compare their Eaton axles to the Ram and the Ford LSD's and open diffs. They pretty much proved that the LSD doesn't provide a ton of traction. The e-locker is the way to go and then you're running an open diff when not engaged.

I've had two previous F-150 4x4's. One had a 3.73 LSD and one had a 3.08 open diff. Neither one felt better to me in snow or mud than the other. Just my 2 cents worth of experience.

 

I agree that the type of driving and how you drive is going to affect gas mileage more than axle ratio for most drivers.

That said, if you had three trucks (all identical except for axle ratio), the truck with 3:31 ratio will achieve the best fuel mileage at highway speeds followed by the 3.55 and 3.73. IMHO, the difference is going to be a nominal amount, especially in mixed driving.

The 3.31 ratio is more than enough for most of the members here as it has the same tow capacities as the 3.55 according to the brochure if I am not mistaken.

The OP wants a rear-locker and get the best fuel economy. If he wants both, he has to get the 3.55's. IMHO, this might be overkill when you get the Lariat trim or higher since you get the 4A AWD system.

It really comes down to what you want/need. How much are you towing? How often? Do you want to be able to accelerate quickly? Most will say get 3.73 gears. My last truck was a 4x2 with 3.08 and it did get 20 MPG on the highway but it was not a rocketship.

Enough rambling, I will let one of the experts weigh in. If I was to buy an EcoBoost, the 3.31 would be enough but I'd prefer a locker so I would opt for the 3.55. Either way, you will have one hell of a truck.

 

I would get the e-locker you get the best of both worlds a selectable locker or when disenaged the standard open diff with the traction control which is more or less better than a limited slip rear end anyways. So go for it 3.55 e-locker.

 

My preference is L/S over E-locker. 3.55 ratio is a good overall ratio and the fuel mileage won't be drastically worse than with a 3.31 ratio. This should be especially true with the 6 speed tranny and the 2 OD ratios. But tires will make the most impact on how a truck performs in snow and ice conditions. With the correct tire choice any option Ford offers will work out ok.

 

That's great to hear thanks! I wonder if it would also be good on the boat ramp? You know the slippery ramps that don't offer all that much traction.

 

I'm sure it would. Especially if you have the e-lock.