Guys,

I've been thru the entire thread, and I can't find what I'm looking for. What change in gas mileage should I expect if I go from 3.55 to 4.10? I read where some readers are getting *BETTER* mpg figures after the change?? (This doesn't make any sense to me.)

Can I just take the ratio 3.55/4.10 and apply it to my current mileage numbers?

Can I drop the original speedo back in with 285x75x16's?

Does the Superchip need reprogramming?

Thanks to all for your help. fish

 

My experience:

Three months after getting the Expedition, I put 285/75R16 tires on it. It came from the factory with 255/70R16s and 3.55:1 gears. After the new tires, the truck seemed to downshift on every hill and even sometimes driving into a strong wind. We drove it that way until this last winter when I had a local 4x4 shop install 4.10s front and back. At the same time the gears were changed, I had them fill the tranny and transfer case with Mobil1 fluids.

Prior to the lower gears, our best fuel economy was just short of 18mpg. This last June we took a trip to VA (from OK) and averaged better than 18mpg... a single tank best of over 20mpg! Around town, mileage has improved by 1 full mpg.

The only reason I can give is that the truck no longer downshifts to go up hills. The gears (and tires) work together to restore the factory gearing and put the engine back into it's powerband. Thus, lower gears are giving better economy.

It off-roads pretty well too!

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1997 4x4 Expedition- 4.6L, true dual exhaust w/glass-packs, K&N air filter, SuperChip, airbox mods, Edelbrock shocks, 285/75R16 BFG ATs, 2000 "XLT" wheels, 4.10 gears, Auburn LS, Clarion In-dash CD player, Smitty Bilt push bars and nerf bars.

2000 4x2 F150 XLT Reg. Cab LWB- 5.4L, Tow Pkg, 3.55LS, CD player,Remote Keyless Entry, Sliding back glass, Special Appearance Pkg., tinted windows, Line-X bedliner, K&N air filter, SuperChip, airbox mods, 285/60R16 Goodyear Eagle GT IIs and Prime #155 wheels.

http://members.visualcities.com/NoMo

 

Nomo- People are finding that once their truck breaks in, the MPGs goes up slightly. This could be one factor with your increased MPG.

All thing being equal, lower gears means higher revs (at the same speed). Higher revs usually mean an increase in gas consumption.

On the other hand, when torque is required (for off line, hills, pulling, whatever), lower gears will mean that you wont have to apply (as much) pedal (fuel volume to the engine), thus better MPG.

Somewhere in all that there is a balance. A balance between gears, tires, shift points and power curves, driving habits and conditions. Go outside the box, mileage will go down.

 

I don't think there is anything more to what riotrob said.

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1999 Red F150 4x4 5.4L XLT X-Cab
Towing Pkg, Corporate 9.75 Rear Axle, 3.55 LS, Corporate 8.8 Front Axle, 3.55 Open, K&N Generation II, JET Chip 32x11.50 Super Swamper SSR
-coming soon
JBA Headers, 40-Series Flomaster exhaust

 

Sorry for any confusion this may have caused. I imagine that I'm the one who GOFISH read about the increased mileage from lower gears. The intent was to show that the large tires had an adverse affect on performance and economy. The gears, despite the logical assumption of hurting economy, actually help in some applications. Without the larger tires, I do expect the fuel mileage to drop when installing lower gears.

The gear swap was performed at 36,000 miles. I'm 99.999% sure that break-in did not cause the economy increase.

 

Thanks for the input, guys!

Now I'm at a loss for what to do... I've got 285x75x16's and understand how Nomo's swap could help. However, most (80%)of *my* driving is on flat ground. While I think I'd miss the torque in hill-driving, I'm not so sure the swap will help me in my pursuit of gas mileage. Damn, I should just eat it and buy the performance.

Does anyone have answers for the other questions? Thanks, again. fish

 

There is one more thing I'd like to point out... The Expedition is a big, heavy 4x4 with the 4.6L engine. A 2WD or 5.4L may not have the downshifting problems that I experienced. I did the gear swap for performance reasons. Although, in the back of my mind, I was hoping to get the results I got.

 

Gofish
riotrob and others are bringing up a good point. First lets face it the X is big and tons of mass.
Before my gear change my X spent a lot of time in 3rd. and down shifted all the time. After my grar change this is what I noticed.
Around town hills lights went from 11.5 to 13
hyway under 70 I now get 16 to 17 about a wash to the old gears
Over 70 is where the rpm's start to kick in and mpg can drop to 14 if I push upper 70.

In ideal conditions with the old gears on flat road cruse control on 70 I could pull 17.5. BUT I dont drive like that! only on vacation trips. The gear change and superchip were my best bag for the buck. Also if you go to bigger tires with your current gear set wow the truck must labor a lot.

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1999 EB X 5.9 4.1 gears, Borla catback, Vortech supercharger,superchip

 

Id like to make another point.

Gears are not normally seen as an MPG mod. Gearing should be looked at by someone looking to increase performance. If all you want is an increase in mileage, look at airbox mods, electric fans, and performance chips first (all at about $200 each). Some people also do exhaust mods, but at $400 I would look to the other mods first.

A lot of people get carried away with their economy figures, while missing the big picture. As an example, lets look at a gearing change. The change costs about $1000 (4x4 apps). Let say this change increases your MPG from 14 to 16 (which it wont, but lets say it does). At $1.50 per gallon of gas, you will save [a whopping] $13.40 over a 1000-mile period. You will need to drive 74K miles to pay off the initial cost of the gear change. Only after the 74K period, will you start to be saving money at the gas pump. And if it was only a 1 MPG increase (from 14 to 15), it will take 140K miles to pay it off.

Something to think about.

 

Aw, hell, who am I foolin'? I'm a performance nut. Why hold back on this one last thing? I drive the 150 a whole 7-8000 miles a year. It's time to bite it and finish this truck up. Besides, the money's burnin' a hole in my pocket

Do you all have any advice on what I'll need to do about the speedo and the Superchip when I make this change?

I thank you all for your help. I really appreciate it! fish

 

The reason you might see a true increase in MPG is two-fold:

Engines have a 'sweet-spot' where fuel consumption is at its best. If, by changing the primary drive ratio, you move your engine's RPM closer to that spot -- you may see an improvement in MPG.

Second, the added leverage afforded by the ratio change may allow you to get the vehicle up to speed (and into top gear) quicker -- thereby improving your efficiency.

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Y2K™ Jim

Toreador Red, Keyless XLT SC SB 5.4L E4x4 4wDisc/ABS, 3.73LS, Skid, HD 7700# Towing, LT-245's on Chrome, Tube-Steps, Captain's, 6CD, Tonneau, named: "Nick"

 

Y2K 7700 4x4,

"...the added leverage afforded by the ratio change may allow you to get the vehicle up to speed (and into top gear) quicker -- thereby improving your efficiency."

Now HERE'S a man whose logic makes sense to me! That's EXACTLY what I'm searching for-better mileage through more torque and hp!!

 

My .02 cents:
I have a 1997 F150 XLT, auto, 4.6, 48000 miles on it. It came with 255-70-16's and 3.55 gears. Always had a 17 MPG mileage, combined city and freeway. After I installed the lift kit (at 45000 miles) and the 285-75-16's the loss of power was very noticeable, even in flat land (Central Texas) or to pass in the freeway and the mileage dropped to about 14 MPG. I truly hated all that downshifting. After I changed to 4.10's I am back at 17 MPG and the good performance is back in there. Again I cruise at 70 MPH at 2000 RPM and it runs very sweet. After this experience I consider that a complete lift should include 3 things: the lift, bigger tires and gear change. There is a trade off to using aftermarket gears: gear whine. I did not have my speedometer calibrated but on the way to work I drive daily by a police radar that shows you your speed, and an indicated 40 MPH in the radar is about 42 in my speedometer. I hope this helps in your decision.
Roberto


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'97 F150 XLT SC, 2WD, 4.6 Auto
* 3" Bullseye spindles
* 2" Superlift angled blocks in rear
* Rancho RS5000's
* AR Baja's 16X8
* Gorilla locknuts (all 20 lugnuts are locknuts)
* 285-75-16 Firestone Wilderness AT III's
* E150 "Triton V8" emblems
* Donmar Sunroof
* Sony CD player
* SuperChip
* K&N Filter
* Bedliner
* Weathertech Ventvisors
* Ford locking gas cap
* Delta aluminum toolbox
* Putco shorty chrome bedrails
* 4:10 US Gear ring & pinion, complete with gear whine.
(It's the Turbo, Son, it's the Turbo!)

 

Roberto-
The 4.10s in our Expedition are as quiet as they can be. You might have the pinion alignment checked on your truck.

 

Nomo:
Did you replace your gears with aftermarket gears, or OEM? (Ford Motorsports?) After I bought my gears from Randy's Ring and pinion I found out that OEM gears do not whine, So I should have done a little more research before buying, and should have ordered from a Ford Motorsports dealer. Overall, it was worth it, gear whine and all.
Roberto