Let’s talk Rear Axle - 4.7 vs 4.46

[Danny's Bronco]

Watch your boost gauge also.
Myself and others have noticed that dropping down a gear(raising RPMs) will keep the motor out of boost while maintaining speed and the fuel mileage increases.
I've manually calculated this over several longer trips and dropping from 6th to 5th, thus raising RPMS to around 2700 was the sweet spot at around 78 mph.
Trying to use 6th just bogs the motor down significantly which forces it to boost and it SLAYS the fuel mileage.
ECO/Boost , choose one.

2.3/manual/4.46/35's

Hey Hoosier Daddy... Is 18.9 mpg what you were able to get after staying out of the boost and trying to get good MPG? I also had 2.3 with the 4.46 and 34.5" tires. I was getting just over 18 mpg and I thought I drove like I stole it. I was always curious if I was wasting a ton of gas. Waiting on my 2dr now so will have to see what it will be like.

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[HoosierDaddy]

Hey Hoosier Daddy... Is 18.9 mpg what you were able to get after staying out of the boost and trying to get good MPG? I also had 2.3 with the 4.46 and 34.5" tires. I was getting just over 18 mpg and I thought I drove like I stole it. I was always curious if I was wasting a ton of gas. Waiting on my 2dr now so will have to see what it will be like.

The stuff at the end of my sig was bone stock, 30" tires etc etc. fuelly averaged for the 5000 miles I kept it stock.
I stopped using that app because I knew the 35's and not correcting the speedo/odo would throw everything way out of wack.

I actually gained fuel mileage swapping up to the 35's when dropping down to 5th on the interstates. A smidge over 20/21 mpg as I recall. I was stunned in disbelief, but I was able to repeat it.

Around town is a different story and I have never manually calculated that out with teh 35's.
I want to say on a fill up it tells me right around 300 to empty ... I could be wrong, I just don't pay that much attention.
Company gave me a work vehicle, so the daughter drives the Bronco more than I get to. LOL!

 

[kodiakisland]

Hey Hoosier Daddy... Is 18.9 mpg what you were able to get after staying out of the boost and trying to get good MPG? I also had 2.3 with the 4.46 and 34.5" tires. I was getting just over 18 mpg and I thought I drove like I stole it. I was always curious if I was wasting a ton of gas. Waiting on my 2dr now so will have to see what it will be like.

Just got back from a 3400 mile trip to MT. Most of my driving is in 5th gear at 78mph. I averaged over 20mpg. Got lucky with very little wind in either direction. Did a trip to ID just a few weeks ago with a lot of headwind at same speeds and averaged a little over 18.

Seems the sweet spot for my Bronco is 5th and 78 as it just settles in a 2700 rpm and runs all day. I've done a lot of 900+ mile days in it now and I pretty much keep it there on the interstate regardless of speed limit.

That's 4.46 gears and 34.5 tires. Will soon have 37s and 4.70 gears, so I'll see how that changes things. Tires will be quite a bit heavier, so I don't expect to stay with the same mileage.

I've done some extended driving below 65mph and impressed with the gas mileage. If one really wants to conserve fuel, go slow. Fill ups on the 2 door estimating over 400 mile range.

 

[indio22]

Just got back from a 3400 mile trip to MT. Most of my driving is in 5th gear at 78mph. I averaged over 20mpg. Got lucky with very little wind in either direction. Did a trip to ID just a few weeks ago with a lot of headwind at same speeds and averaged a little over 18.

Seems the sweet spot for my Bronco is 5th and 78 as it just settles in a 2700 rpm and runs all day. I've done a lot of 900+ mile days in it now and I pretty much keep it there on the interstate regardless of speed limit.

That's 4.46 gears and 34.5 tires. Will soon have 37s and 4.70 gears, so I'll see how that changes things. Tires will be quite a bit heavier, so I don't expect to stay with the same mileage.

I've done some extended driving below 65mph and impressed with the gas mileage. If one really wants to conserve fuel, go slow. Fill ups on the 2 door estimating over 400 mile range.

The engine rpm difference at cruise is so small between 4.46 and 4.70 diffs. Something like 150rpm? So regardless of 4.46/4.70, with 35s is the 6th gear usable? Seems odd if not, because Ford supplies the Sas with 35" tires and 4.70. It surprises me Ford didn't switch to a deeper diff gear than 4.70 for the 35s.

 

[kodiakisland]

The engine rpm difference at cruise is so small between 4.46 and 4.70 diffs. Something like 150rpm? So regardless of 4.46/4.70, with 35s is the 6th gear usable? Seems odd if not, because Ford supplies the Sas with 35" tires and 4.70. It surprises me Ford didn't switch to a deeper diff gear than 4.70 for the 35s.

Yeah, the difference is negligible, and practically the same at 4.46/35 and 4.70/37.
I wanted to go 5.13s, but finally decided I can't afford to go with the Dana 44 upgrade. For less than the D44 front axle and CVs, I can buy both front and rear axles with lockers in 4.70, and buy the 3.0 steering rack. Then I have a full set of 4.46 axles with rear locker to sell.

I won't be getting as low of gears as I want, but will be upgrading to a stronger front axle and gaining a front locker.

As far as 6th gear being usable, for me it is not. I'm at almost 30K miles and have been in 6th less than 5 times ever. For trims with 30-32 inch tires, maybe more so.

 

[8ronco]

Watch your boost gauge also.
Myself and others have noticed that dropping down a gear(raising RPMs) will keep the motor out of boost while maintaining speed and the fuel mileage increases.
I've manually calculated this over several longer trips and dropping from 6th to 5th, thus raising RPMS to around 2700 was the sweet spot at around 78 mph.
Trying to use 6th just bogs the motor down significantly which forces it to boost and it SLAYS the fuel mileage.
ECO/Boost , choose one.

2.3/manual/4.46/35's

2.3 manual with 37's - agree 100%, 6th gear is utterly useless and kills fuel economy. 2700 rpm in 2nd, 3rd, 4th or 5th for the best economy.

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