dewser

I am sure someone has asked or discussed this before, but I am damned if I can find it. What I am wondering is the guys that have a 3.5 in a screw 4X4 with the 3.31 how they like it. I am seriously considering this combination as I do not tow a lot of weight and do a fair amount of highway and city driving. My train of thought is that it would get pretty good mileage all around. Thanks for any insight into this.. I have done a ton of reading on here and think it's an awesome board !!

2011BLK_SCREW

Most of the posts on here are comparing 3.5 to the 3.73
not really a gearing expert but from reading around pretty much the 3.31 should get better mpg than an identical truck with a higher gear, but at the expense of acceleration and towing( which you already mentioned you dnt do a lot of) Howver, the difference between the 3.5 to 3.31 seems minimal, eeven less than that between the 3.5 to 3.73 (.23>.19) from other threads comparing the 3.5 to 3.73 that small difference in axle rotaion rartio seemed to only deliver a slight mpg advantage to the lower gears. Im sure over the long run the small mpg gain will pay off if you already know what your truck is going to be used for. all that being said, this is for a completely stock truck. once you start adding bigger tires a higher gear will be prefered to get your final ratio back as close to stock as possible.

DieselDawg

3.5 is the ecoboost ... 3.55 is the rearend

If towing is not a big concern, the 3.5L EB would probably do fine with 3.15's or 3.31's with all the low rpm torque. If you tow, the 3.55's or 3.73's would probably suit you better.

KIETH F150

that is the best way to go! EB with 3.31s
I had 4.6L 3.31 gear 35" tire and towed 2000lbs trailer daily on problem!

Ford850

I've read some feedback from owners of that cobo and they seem to love it or hate it. I would guess it would feel like the next step above the 3.7, with more cruising power when you want it.

papa tiger

The difference between 3.31 and 3.73 is 4/10 of a turn of the pinion which would translate to like having a 7th gear in the trans/overdrive. Add to it 35 inch tires and like adding an 8th overdrive gear. If you plan big tires go with 3.55. If you heavy haul go with a truck differential 3.73 and big wheels. There is no substitute for the big gears of a 3.73 when dragging atv's around. Your axles will live longer with mightier gears. Also talken mud and deep snow. Lots more fun with the mightier axle. More control on icy surfaces. Light 3.31/car axle ok for work to home truck.

bubbabud

$.02 worth. I have 3.5 ECO with the standard tow package [8800lbs]stock tires 265x60 R18 and 3.15 gears I pull a16ft flatbed trailer with a full body jeep JK and trail gear 6000lbs total up from phoeinx to Flagstaff AZ several 6% grades at 70mph with no Issues I dont plan to install larger tires so I specked the tallest gear I could get. the low end torque of the EB makes it a breeze. The only down side is I have to put up with MUCH better MPG and I dont get to go to the gas station as often. If your going to tow heavy or big boxy loads you would be better served with lower gears but for my purpose + economy 3.15s work great. Bubbabud

CDC5.0

I have 5.0L with the 3.31, and my engine makes 40 ft-lbs of torque less then the ecoboost (380 vs 420) and it does just fine. I can pull my parents 5500lb camper around no problem.

HunterSmitty

3.31 gears work fine for me, and I haul my ATV alot and pull a couple bikes on a trailer. If I was towing more than 5000lbs, I'd prolly go to the 3.55 gearing, but 3.31 was the best fit for me for all around better mileage, and still has loads of power. I very rarely ever shift out of 6th gear on any grades I take unloaded.

superccs

I avoided getting the 3.15 and 3.31 gears in favor of the 3.55 because I knew I would be getting bigger tires and probably would haul some massive loads. But like many have said the EB engine, like the honey badger, " ."