Rear end gearing

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Rear end gearing

Sideflop
In my F250's current state, it has axle code 73 (pretty sure that's a Dana 60 rear end with 3.54s), and the truck gets about 15-18 mpg going 65-75 mph. I'm sure that I'll be using it to haul or tow stuff occasionally. Would it be good to keep 3.54s, or is there a better rear end I should know about?

Nathan
1984 F250 XL with International 6.9L IDI, Borg Warner T19 transmission and Borg Warner 1345 transfer case. Dana 50 limited slip front end, Dana 70 open rear end with 3.73 gears
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Re: Rear end gearing

Gary Lewis
Administrator
Yes, the 73 does indicate 3.54 gears.  That's what Big Blue has and he's spinning ~2500 RPM at 65 MPH, which isn't conducive to decent MPG.  But, he'll tow anything quite happily in 4th gear at that speed.

So I think the issue is not in the axle ratio but in not having an overdrive gear.  We both need the engine turning in that range when working hard, but it sure would be nice to get better MPG - although your 15 - 18 MPG is already pretty decent when compared to my 11 - 12 MPG.  Anyway, that would take dropping the RPM when cruising w/o a load.  And that takes a tranny with OD.

Toward that end I'm installing a ZF5 behind Big Blue's 460.  That'll give me the 2500 RPM at 65 MPH in 4th for towing, but drop it to 1900 in 5th for cruising.  And then I might get 14 MPH.  
Gary, AKA "Gary fellow": Profile

Dad's: '81 F150 Ranger XLT 4x4: Down for restomod: Full-roller "stroked 351M" w/Trick Flow heads & intake, EEC-V SEFI/E4OD/3.50 gears w/Kevlar clutches
Blue: 2015 F150 Platinum 4x4 SuperCrew wearing Blue Jeans & sporting a 3.5L EB & Max Tow
Big Blue: 1985 F250HD 4x4: 460/ZF5/3.55's, D60 w/Ox locker & 10.25 Sterling/Trutrac, Blue Top & Borgeson, & EEC-V MAF/SEFI

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Re: Rear end gearing

Sideflop
In reply to this post by Sideflop
Cool, thanks for the info.
Nathan
1984 F250 XL with International 6.9L IDI, Borg Warner T19 transmission and Borg Warner 1345 transfer case. Dana 50 limited slip front end, Dana 70 open rear end with 3.73 gears
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Re: Rear end gearing

Steve83
Banned User
In reply to this post by Sideflop
Within a fairly wide range, RPM is NOT directly related to MPG.  Making the engine spin slower will make it work harder (higher compression/more throttle/more fuel per combustion event) to push the same truck over the same mile.

15-18MPG is pretty good for any F250; especially a 35-year-old diesel 4WD.  If you want to increase it slightly, air up the tires, remove all unneeded weight, and drive like there's a tall wine glass on the dash - don't spill it (no hard acceleration, braking, or steering).
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Re: Rear end gearing

1986F150Six
Administrator
Please understand that I am not being argumentative, as that is not my nature, but I do think engine speed can and does make a difference in fuel mileage.

With over 10 years of records as my truck is driven the same distance and route to and from work, the normal gas consumption is ~17+ mpg. Approximately 50% of this is @ 45 mph [the rest is stop and go]. At 45 mph, the truck can be in OD @ ~1200 RPMs.

Experimentation has shown that if OD is not used for the entire tank, the mileage drops to 15+ mpg. While in 3rd gear @ 45 mph, the RPMs are ~1675. Looking at the vacuum gauge reveals that the vacuum is greater when cruising in 3rd vs. OD.

Pumping losses take an effect.
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Re: Rear end gearing

Gary Lewis
Administrator
David - Agreed.

The 80's were a 'tween time for trucks.  The lighter trucks, like the F100's and some of the F150's, got really high gearing in a quest for MPG.  For instance, the 1983 Fuel Saver Package got 2.47:1 gears, as shown on Page 28 of the 1983 Dealer Facts Book on the Vehicles and then 4x2 tabs.  However, as David has explained before, while those gears gave good MPG, they weren't fun to drive as you had to downshift if there was a hill in sight.

But, since the HD trucks were meant for towing and hauling, they needed more reasonable gearing, like 3.54's.  Unfortunately Ford didn't have transmissions with overdrive available for the big engines in the early part of the 80's.  In fact, it wasn't until 1987 when the ZF5 came out that the 460 and diesel trucks had an OD manual tranny available, and it wasn't until '89 that there was an automatic with OD available for those engines.

Ford wouldn't have gone to the expense of making transmissions with overdrive gears available if they didn't help on the MPG.  And they help because of two things.  One, the higher the engine RPM the more internal friction there is.  Second, as David said, the higher the vacuum the higher the pumping losses.  Or, to say it another way, the lower the vacuum (due to gear selection) the lower the pumping losses are and, therefore, the higher the efficiency.

Here's a quote from Hard Working Trucks:

“Lower (higher numerically) axle ratios such as the 3.73s and 4.10s, provide the best acceleration and towing performance in pickups,” says Dawn Piechocki, Ford’s Vehicle Engineering Manager for the new F-150s, Expeditions and Navigators.

“But in real-world driving, unladen, those lower ratios cost about 2 mpg in highway fuel economy compared to 3.15s, which is the ratio [Ford] uses in pickups when trying to maximize mpg,” says Piechocki. “But in city driving the lower axle ratios have little effect of fuel mileage.”

And, in fact the 2 mpg difference is about the penalty I see on Blue by having spec'd the Max Tow package, which gave me 3.55 gears.  I've checked with others that didn't tick that box and, therefore, got the taller 3.15 gears and they do get better MPG.


Gary, AKA "Gary fellow": Profile

Dad's: '81 F150 Ranger XLT 4x4: Down for restomod: Full-roller "stroked 351M" w/Trick Flow heads & intake, EEC-V SEFI/E4OD/3.50 gears w/Kevlar clutches
Blue: 2015 F150 Platinum 4x4 SuperCrew wearing Blue Jeans & sporting a 3.5L EB & Max Tow
Big Blue: 1985 F250HD 4x4: 460/ZF5/3.55's, D60 w/Ox locker & 10.25 Sterling/Trutrac, Blue Top & Borgeson, & EEC-V MAF/SEFI

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Re: Rear end gearing

1986F150Six
Administrator
Gary Lewis wrote

And, in fact the 2 mpg difference is about the penalty I see on Blue by having spec'd the Max Tow package, which gave me 3.55 gears.  I've checked with others that didn't tick that box and, therefore, got the taller 3.15 gears and they do get better MPG.

But, can those "others" effortlessly pull Big Blue on a trailer @ 75 mph?
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Re: Rear end gearing

Gary Lewis
Administrator
LOL!  Not as easily, that is for sure.

So, let me add to my statement.  I'm glad that I picked the Max Tow package.  I spec'd Blue to tow, and tow it will, with ease.  As David said, my brother and I made a mad dash to Florida to get Big Blue, and towed him back through the night at 75 MPH.  My brother was amazed at how easily it did it.  No muss, no fuss.

Yes, I'd get better MPG with taller gearing.  But I bought the truck to tow our boat and my car-hauler trailer, which is does superbly, and not to get the best MPG.  To date I know of 5,000 miles of towing it has done in two trips - taking our 25' Sea Ray to Lake Powell and back, getting 11.0 MPG at a relaxed 65 MPH, and bringing Big Blue back and getting 9.0 MPG.  Plus many shorter trips, like taking the trailer to Kansas to get the D60.

And our daughter is tentatively planning a road trip using it to tow a camping trailer of some kind next summer, and I know it'll do the job for them very nicely.  So, I spec'd it correctly.
Gary, AKA "Gary fellow": Profile

Dad's: '81 F150 Ranger XLT 4x4: Down for restomod: Full-roller "stroked 351M" w/Trick Flow heads & intake, EEC-V SEFI/E4OD/3.50 gears w/Kevlar clutches
Blue: 2015 F150 Platinum 4x4 SuperCrew wearing Blue Jeans & sporting a 3.5L EB & Max Tow
Big Blue: 1985 F250HD 4x4: 460/ZF5/3.55's, D60 w/Ox locker & 10.25 Sterling/Trutrac, Blue Top & Borgeson, & EEC-V MAF/SEFI

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Re: Rear end gearing

85lebaront2
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FWIW, very good friend has a 1995 F350 2WD crew cab dually with the Powerstroke 7.3L, E4OD and 4.10 gear, he gets 14 mpg normally and it doesn't seem to vary much with weight, air drag yes. Darth is a 1986 similar truck but 460 converted to EFI (but still has the deep dish pistons) and E4OD with a 3.55 gear. Right now I get an average of around 11 mpg, but have been as high as 12.5 on a nice high speed (70 mph) drive to W VA to my son's. New engine going in is 9.3:1 compression and mild cam.

I am hoping to get up around his fuel economy, as far as towing, I hauled a 10K 5th wheel trailer, original owner was a horse breeder and hauled some big trailers. Even with the very low compression, I can stomp the throttle from a standing start and spin all 4 rear wheels.
Bill AKA "LOBO" Profile

"Getting old is inevitable, growing up is optional" Darth Vader 1986 F350 460 converted to MAF/SEFI, E4OD 12X3 1/2 rear brakes, traction loc 3:55 gear, 160 amp 3G alternator Wife's 2011 Flex Limited Daily Driver 2009 Flex Limited with factory tow package Project car 1986 Chrysler LeBaron convertible 2.2L Turbo II, modified A413

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Re: Rear end gearing

Gary Lewis
Administrator
Big Blue currently gets 11+ on the highway, but he only has the T19 with 1:1 top gear, as opposed to the .71:1 of your E4OD.  So where you are turning ~1800 RPM @ 65 MPH I'm turning 2500.  And I'm hoping, like you, that with the ZF5, EFI, and a better engine Big Blue will get about 14 MPG.  If so, we will have some of the most efficient 460's around.  
Gary, AKA "Gary fellow": Profile

Dad's: '81 F150 Ranger XLT 4x4: Down for restomod: Full-roller "stroked 351M" w/Trick Flow heads & intake, EEC-V SEFI/E4OD/3.50 gears w/Kevlar clutches
Blue: 2015 F150 Platinum 4x4 SuperCrew wearing Blue Jeans & sporting a 3.5L EB & Max Tow
Big Blue: 1985 F250HD 4x4: 460/ZF5/3.55's, D60 w/Ox locker & 10.25 Sterling/Trutrac, Blue Top & Borgeson, & EEC-V MAF/SEFI

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Re: Rear end gearing

grumpin
Gary Lewis wrote
Big Blue currently gets 11+ on the highway, but he only has the T19 with 1:1 top gear, as opposed to the .71:1 of your E4OD.  So where you are turning ~1800 RPM @ 65 MPH I'm turning 2500.  And I'm hoping, like you, that with the ZF5, EFI, and a better engine Big Blue will get about 14 MPG.  If so, we will have some of the most efficient 460's around. 
 That’s funny right there!
Dane
1986 F250HD SC XLT Lariat 4x4 460 C6-Sold
1992 Bronco XLT 4x4 351W E4OD
1998 GMC Sierra SLE K1500 350 4L60E
Arizona
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Re: Rear end gearing

Gary Lewis
Administrator
Yeah, it was meant that way.  But in reality it is pathetic.  
Gary, AKA "Gary fellow": Profile

Dad's: '81 F150 Ranger XLT 4x4: Down for restomod: Full-roller "stroked 351M" w/Trick Flow heads & intake, EEC-V SEFI/E4OD/3.50 gears w/Kevlar clutches
Blue: 2015 F150 Platinum 4x4 SuperCrew wearing Blue Jeans & sporting a 3.5L EB & Max Tow
Big Blue: 1985 F250HD 4x4: 460/ZF5/3.55's, D60 w/Ox locker & 10.25 Sterling/Trutrac, Blue Top & Borgeson, & EEC-V MAF/SEFI

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Re: Rear end gearing

Nothing Special
In reply to this post by Steve83
Steve83 wrote
Within a fairly wide range, RPM is NOT directly related to MPG.  Making the engine spin slower will make it work harder (higher compression/more throttle/more fuel per combustion event) to push the same truck over the same mile....
Gary Lewis wrote
....  Ford wouldn't have gone to the expense of making transmissions with overdrive gears available if they didn't help on the MPG.  And they help because of two things.  One, the higher the engine RPM the more internal friction there is.  Second, as David said, the higher the vacuum the higher the pumping losses.  Or, to say it another way, the lower the vacuum (due to gear selection) the lower the pumping losses are and, therefore, the higher the efficiency....
With a gas engine lower vacuum (more open throttle) gives more efficiency, partly because of the reduced pumping loses, the engine doesn't have to work to pull air past the closed throttle plate.  Back in a college Internal Combustion Engines lab we calculated BSFC (Brake Specific Fuel Consumption) on an old Ford 6 cylinder and found to our surprise (but not the instructors) that the engine made the most of the fuel it burned at wide open throttle.  Looking at the power band of the engine and assuming needing 15 horsepower to maintain 55 mph we figured it would get the best mileage in a steady-state cruise with a final drive ratio of something like 1.5:1!  Now that was that engine which was pretty much a low end torquer, and it was looking at steady state cruise, not real-world accel/decel/hill/stop kind of driving.  When all of that is taken into account Steve's position is closer to the truth.  But engine speed does hurt a gas engine.

Diesels don't have throttle plates, so they don't experience the same pumping losses at low "throttle" that gassers do.  And I don't have any lab experience with diesels to draw on.  But I did have a 2002 F-350 with a 7.3L PowerStroke that used more fuel (measured in dollars) than my '97 with a 460.  So I played around with it to figure out whatever I could.  It had a trip computer that displayed average fuel mileage.  So on one road trip I set the speed control at 55 mph and then at somewhere around 70 mph, in both 3rd and 4th gears (4 speed automatic).  I picked the upper speed because it have me the same engine rpm in 4th gear that I had at 55 mph in 3rd gear.  Steady state cruise on flat level ground I got about 21 mpg at 55 mph in 4th gear, 16 mpg at 55 mph in 3rd gear, 15 mpg at ~70 mph in 4th gear and ~11 mpg at 70 mph in 3rd gear.

The most amazing thing to me about that was how much more engine speed affected mileage than vehicle speed did.  Speeding the engine up by increasing vehicle speed in 4th gear from 55 to ~70 cost me only 1 more mpg than the same increase in engine speed by downshifting to the same higher engine speed and keeping the same vehicle speed.

Surprising but true.

(And no, I didn't get 21 mpg at 55 mph with that truck except in a steady flat cruise.  On a highway (not freeway) trip at 55 mph I might average 14 mpg.  Overall I was closer to 12~13 mpg, and since it burned more expensive diesel fuel, my 460 at 10~11 mpg is generally cheaper to drive.)
Bob
Sorry, no '80 - '86 Ford trucks
"Oswald": 1997 F-250HD crew cab short box, 460, E4OD, 4.10 gears
"Pluto": 1971 Bronco, 302, NV3550 5 speed, Atlas 4.3:1 transfer case, 33" tires
"the motorhome": 2015 E-450-based 28' class C motorhome, 6.8L V-10
"the Dodge": 2007 Dodge 2500, 6.7L Cummins
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Re: Rear end gearing

1986F150Six
Administrator
<quote author="Nothing Special">
Steve83 wrote
With a gas engine lower vacuum (more open throttle) gives more efficiency, partly because of the reduced pumping loses, the engine doesn't have to work to pull air past the closed throttle plate.  Back in a college Internal Combustion Engines lab we calculated BSFC (Brake Specific Fuel Consumption) on an old Ford 6 cylinder and found to our surprise (but not the instructors) that the engine made the most of the fuel it burned at wide open throttle.  Looking at the power band of the engine and assuming needing 15 horsepower to maintain 55 mph we figured it would get the best mileage in a steady-state cruise with a final drive ratio of something like 1.5:1!  Now that was that engine which was pretty much a low end torquer, and it was looking at steady state cruise, not real-world accel/decel/hill/stop kind of driving.  When all of that is taken into account Steve's position is closer to the truth.  But engine speed does hurt a gas engine.
Good stuff, Sir!

My son's 1984 F150 with 4.9L, 4 speed manual O.D. and small factory air dam on front bumper was "born" with 2.47 rear gears. [2.47 X .71 O.D. = 1.75]

Before gasohol, this truck routinely returned 26+ mpg @ 55-60 mph.
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Re: Rear end gearing

Ray Cecil
In reply to this post by Gary Lewis
Factors in mpg:
Torque @ rpm
Vehicle weight
Vehicle speed
Wind direction
Wind speed
Humidity
Air temperature
Elevation
Tire pressure
Tune/timing
Condition of engine/trans
Wind resistance/ drag coefficient
Vehicle height
Tire circumference
Tire tread pattern
Suspension alignment
Condition of bearings
Proper release on brake shoes and calipers
Driver habits
Ac and accessories being engine driven, on or off
Fuel grade/mix
Engine modifications
Engine air/fuel ratio and its devices that control it. (Carb vs injection)

Im probably missing something. However, its impossible to do a proper scientific expirement in the real world on real roads while any or all of these conditions can change. That is why laboratories exist that control all these conditions to isolate each variable. Dave's road tests are good, but I highly doubt he is controlling for all factors. Id say his results are suggestive, rather than conclusive.
1988 F250 Supercab Longbed 7.3 IDI, C6, 1356, GEARVENDORS, 4.10 Sterling with autolocker

1986 F150 302, C6, 9" 2.75, Wood Flatbed


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Re: Rear end gearing

Gary Lewis
Administrator
In reply to this post by Nothing Special
Bob - I'm jealous of you getting to go into the lab.  I didn't take ICE as I was in EE, but a buddy of mine did take it and I bought the textbook from him - and have read it multiple times.  But, I didn't get to go into the lab.  

Anyway, you make a good point about a diesel not having a throttle, so technically not having "pumping losses".  So I was wrong when I mentioned that as an issue since Sideflop's engine is the IDI.  But, you did prove that the RPM does make a significant difference, regardless of whether it is pumping losses or something else.  Phrasing your data differently, and assuming you had the E4OD with 3.55 gears:

55 MPH: In 4th you were turning 1500 RPM and got 21 MPG.  But by shifting to 3rd you were turning 2100 RPM and dropped to 16 MPG.  That's a 24% reduction in MPG

70 MPH: In 4th you were turning 1900 RPM and got 15 MPG, but dropping to 3rd gear you were turning 2700 RPM and got 11 MPG.  This is a 27% reduction in MPG.

Granted this wasn't an exhaustive test, but my understanding is that the ECU was doing the calculations based on the amount of fuel it was injecting into the engine, so your load, weather, type of fuel, etc wasn't changing much.  Therefore it should be very indicative of the kinds of MPG change that would be seen by changing axle gears.
Gary, AKA "Gary fellow": Profile

Dad's: '81 F150 Ranger XLT 4x4: Down for restomod: Full-roller "stroked 351M" w/Trick Flow heads & intake, EEC-V SEFI/E4OD/3.50 gears w/Kevlar clutches
Blue: 2015 F150 Platinum 4x4 SuperCrew wearing Blue Jeans & sporting a 3.5L EB & Max Tow
Big Blue: 1985 F250HD 4x4: 460/ZF5/3.55's, D60 w/Ox locker & 10.25 Sterling/Trutrac, Blue Top & Borgeson, & EEC-V MAF/SEFI

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Re: Rear end gearing

Nothing Special
Gary Lewis wrote
Bob - I'm jealous of you getting to go into the lab.  I didn't take ICE as I was in EE, but a buddy of mine did take it and I bought the textbook from him - and have read it multiple times.  But, I didn't get to go into the lab.  

Anyway, you make a good point about a diesel not having a throttle, so technically not having "pumping losses".  So I was wrong when I mentioned that as an issue since Sideflop's engine is the IDI.  But, you did prove that the RPM does make a significant difference, regardless of whether it is pumping losses or something else.  Phrasing your data differently, and assuming you had the E4OD with 3.55 gears:

55 MPH: In 4th you were turning 1500 RPM and got 21 MPG.  But by shifting to 3rd you were turning 2100 RPM and dropped to 16 MPG.  That's a 24% reduction in MPG

70 MPH: In 4th you were turning 1900 RPM and got 15 MPG, but dropping to 3rd gear you were turning 2700 RPM and got 11 MPG.  This is a 27% reduction in MPG.

Granted this wasn't an exhaustive test, but my understanding is that the ECU was doing the calculations based on the amount of fuel it was injecting into the engine, so your load, weather, type of fuel, etc wasn't changing much.  Therefore it should be very indicative of the kinds of MPG change that would be seen by changing axle gears.
It was an '02 truck, so not an E4OD.  I'm not sure what trans it had, but that's not that important for the overall lessons (and as Ray points out, this experiment wasn't taking nearly everything into account, so that's all there is to gain here: overall lessons).  And it had 3.73 gears (again, for what that's worth...).

But the only real correction I'd make to your phrasing is that 3rd gear at 55 mph and 4th gear at whatever speed I was going (somewhere around 70) were the same engine speed on my tach.  I was trying to see how much vehicle speed vs engine speed affected my mileage, so I aimed for the same engine speed.

And yes, this was done during a period of maybe 20 minutes as I drove down a pretty flat, straight, boring piece of highway.  Wind speed and direction changes were pretty minimal, and essentially no elevation changes so hills weren't a factor.  Pretty much no other changes other than vehicle and engine speed.

But I would caution against looking at these big percentages and thinking they might indicate what changes in mileage you could expect with gearing changes.  Again, the 21 mpg in 4th at steady-state 55 mpg translated to only around 14 mpg in real life 55 mph driving.  While dropping to 3rd at steady-state 55 mph dropped to around 16 mpg, I doubt the real world 55 mph driving like that would have dropped nearly as much, maybe from 14 to 12 mpg or so???  Just saying be careful not to extrapolate this too far.  But yes, engine speed does affect fuel consumption.
Bob
Sorry, no '80 - '86 Ford trucks
"Oswald": 1997 F-250HD crew cab short box, 460, E4OD, 4.10 gears
"Pluto": 1971 Bronco, 302, NV3550 5 speed, Atlas 4.3:1 transfer case, 33" tires
"the motorhome": 2015 E-450-based 28' class C motorhome, 6.8L V-10
"the Dodge": 2007 Dodge 2500, 6.7L Cummins
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Re: Rear end gearing

Gary Lewis
Administrator
Bob - Good points.  You did say that the instantaneous MPG you were getting was far better than the average MPG the truck returned, so it isn't reasonable for anyone to expect to get MPG's like the instantaneous readings.

However, what you showed is that gearing does matter.  Your transmission should have been the 4R100, which had the same gear ratios as the E4OD.  So let's redo my rephrasing of your test using the 3.73 gear ratio and same engine speeds for 3rd @ 55 MPH and 4th at whatever:

55 MPH:  In 4th you were turning 1579 RPM and got 21 MPG.  But by shifting to 3rd you were turning 2224 RPM and dropped to 16 MPG.  That's a 24% reduction in MPG

77 MPH: In 4th @ 77 MPH you'd be turning 2224 RPM, the same as in 3rd at 55 MPH.  And at that RPM you were getting 16 MPG.  And by pulling it down into 3rd at that speed you were turning 3113 RPM, which reduced the MPG to 11, which is a 27% reduction.

It is interesting, at least to me, to note that the gear ratio change is 29%.  In other words, 3rd is 1:1 and 4th is .71:1.  So a 29% change in engine speed got a bit less than that in MPG - under steady-state conditions.  But under stop and go conditions the overall MPG is far less.

However, if you got 16 MPG at 55 MPH using 4th and it dropped to 12 MPG by using 3rd, that would be a 25% drop.  Just saying.....  
Gary, AKA "Gary fellow": Profile

Dad's: '81 F150 Ranger XLT 4x4: Down for restomod: Full-roller "stroked 351M" w/Trick Flow heads & intake, EEC-V SEFI/E4OD/3.50 gears w/Kevlar clutches
Blue: 2015 F150 Platinum 4x4 SuperCrew wearing Blue Jeans & sporting a 3.5L EB & Max Tow
Big Blue: 1985 F250HD 4x4: 460/ZF5/3.55's, D60 w/Ox locker & 10.25 Sterling/Trutrac, Blue Top & Borgeson, & EEC-V MAF/SEFI

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Re: Rear end gearing

Nothing Special
Gary Lewis wrote
....  However, if you got 16 MPG at 55 MPH using 4th and it dropped to 12 MPG by using 3rd, that would be a 25% drop.  Just saying.....  
After I posted that I wondered what percentage the number I arbitrarily picked gave!  But I actually only got about 14 mpg in real-world 55 mph driving, so my arbitrary guess at 12 mpg in 3rd is only a 14% drop.  But my real point is that it was an arbitrary guess, and it probably would've been significantly less than a 29% drop.

For what it's worth, everyone told me that I should've been getting high teens in real-world mileage with that truck.  But I didn't.  Based on this test I think the axle gearing was a big part of that.  That big turbo diesel could've easily pulled 3.55 gears, if not 3.23 or even taller.  I'm sure it would've done better like that.  And the shift points for the auto trans were at least 5 if not 10 mph higher than they should've been in normal driving.  I tried using a really light foot, or letting up on the accelerator when I wanted it to shift, but there was just no way to get it to upshift until that big diesel was roaring.  Loading it down was another place the shift points were terrible.  That engine could've easily lugged down in 4th going up a hill on a 55 mph highway, but even unloaded on hills that weren't all that steep it would unlock the torque converter and drop into 3rd.  So with as sensitive as the fuel mileage was to engine speed, there was no way to keep the engine speed down in real-world driving.  Did I mention that I hated that truck?
Bob
Sorry, no '80 - '86 Ford trucks
"Oswald": 1997 F-250HD crew cab short box, 460, E4OD, 4.10 gears
"Pluto": 1971 Bronco, 302, NV3550 5 speed, Atlas 4.3:1 transfer case, 33" tires
"the motorhome": 2015 E-450-based 28' class C motorhome, 6.8L V-10
"the Dodge": 2007 Dodge 2500, 6.7L Cummins
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Re: Rear end gearing

Gary Lewis
Administrator
Sometimes computers seriously hinder attempts to maximize economy.  On Blue there's no way to lock it in a higher gear w/o placing it in Manual mode, and then you'd better stay on top of things closely.  But, it can be done and you can get deep into the turbo before allowing it to shift.

I'd wondered about doing that on our vacation where we towed the Sea Ray to Lake Powell.  In the end I just locked it out of 6th for the most part, save for looooooong downhill runs, and let it do its own thing shifting down from there.

Anyway, at least the newer trucks have that ability.  And, with my Mongoose cable and Core Tuning software I can reprogram the E4OD for Dad's truck for shift points, lock/unlock points, etc.  Bill's done that already on Darth.
Gary, AKA "Gary fellow": Profile

Dad's: '81 F150 Ranger XLT 4x4: Down for restomod: Full-roller "stroked 351M" w/Trick Flow heads & intake, EEC-V SEFI/E4OD/3.50 gears w/Kevlar clutches
Blue: 2015 F150 Platinum 4x4 SuperCrew wearing Blue Jeans & sporting a 3.5L EB & Max Tow
Big Blue: 1985 F250HD 4x4: 460/ZF5/3.55's, D60 w/Ox locker & 10.25 Sterling/Trutrac, Blue Top & Borgeson, & EEC-V MAF/SEFI

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