I have an 04 screw with 5.4L 3v, with 3.55 gears, with the factory tow package, My mileage is around 11-13 mpg around town. I have read others with 3.73 gears and other that seem to get better mileage, what do the gears do? How expensive would it be to change them?
Thanks,
Doug

 

The cost of the gear swap is major. You are looking at 1500-3000. How many miles do you have? What octane do you use? Any mods? What kind of driving do you regularly see?

 

I have the 2005 Fx4 scab 5.4 w/3.73 diff,. With 1,400 now miles and getting 13.99 In town & 19.0 on the first 220 mile @ 65mph hiway trip burning 11.59 gal. The 3.73 gears are lower than your 3.55.. I think It,s the differance with your driving style and mine...???
Doug M.

 

After commuting over 800 miles/week for 8 years, I was looking for good highway mileage, so I got 3.55's. Now I've moved closer to work (15miles) and am getting killed by high MPG...I don't see the highway anymore!! It's all stop signs, lights, school zones, etc. Constant start...stop...start...stop.

I'm seriously thinking of putting 4.10's in. I've priced front/rear gear sets for $800, and have a moonlighting Ford tech who'll put 'em in for another $800.

But $1,600 can buy A LOT of gas, so I'm not really sure if I'll go for it. I do plan on keeping this truck til it's (or mine) dying day.

 

Have you thought about a tuner Don? I gained about 1.4mpg with my Superchips. With the addition of the tonneau, Im at 2+ above stock. My 01 FX4 had 3.55s, and I averaged 17mpg. With my 04 and 3.73s, I average 17..with much more power.

 

I've thought about it, but I'd keep it an 87 octane program (don't want to pay 10 cents extra for each precious gallon!).

I know tuner pros/cons have been beaten to death, but I'm still not sold on the value unless you go to a higher octane. And that, to me, would cancel out any benefit.

I don't really want more power, just better MPG's. So I figure a better mechanical advantage through a gear change. Or will a tuner give me what I want??

 

The extra 4 dollars a fillup for a much better vehicle (IMHO) is worth it to me. Theoretically, the better mechanical advantage would help. You would have to crunch the numbers though. You might find that with the lower gears, your 'normal' rev around town might be increased...and yielding worse mileage! It all comes down to what you said about $1600 buying A LOT of gas. Ive noticed that I get into my gas less around town. The truck works with the power it has much more efficiently, and I dont have to get into the pedal nearly as often. I would also be a liar to say that I dont love the firmer shifts, and throttle response.

 

Well, Rich...because I respect your opinion, I'm browsing the "Chips and Tuners" forums right now to get a better understanding. I know you were pleased with your tuner when you first installed it in your '04, so maybe I'll open my mind to different alternatives.

Thanks for your help! But I'm still going to follow this thread to see what other thoughts are out there....!

 

I was under the impression that lower gears gave the best gains for MPG. IOW the 3.55 gears should give you better gas mileage than the 4.10s. The 4.10s will give you more torque and power?

 

Its all a function of tire size, gears, rpms, and driving conditions. It isnt easy to use a blanket statement for lower gears. Yes, under many conditions, you can yielded better mpg with lower gears (like if you tow alot, or you have moved to larger tires).

 

Oh, and I think you are using the term "lower" incorrectly. "Lower" gears refer to gears that are numerically larger (4.10 is larger/lower than 3.55), and provide greater mechanical advantage.

 

Just for those that read this thread and get a little confused;
You guys who have been swapping gears, and cams since you were nine, can ignore this.

The language is lousy for understanding this subject.

Lower gears mean higher numbers, higher gears mean lower numbers.

The higher the number the lower the gears.

Old rules were to get better mileage, you put in a higher gear (lower number) and the engine turned less RPM's thus using less gas. You had less power, for the same reason you have less power in third than in second.

Lower gears were just to maximize the engines power, thus getting more torque and horsepower at lower speeds.

Most engines make most of their horsepower way up above the RPM's that you see everyday. By making more horsepower lower, coupled with the lower gear ratio, dropping the gears from 3.55 to 4.10 should make a huge difference in power.

So old school, put lower gears (higher numbers) and it's like dropping each gear down half a gear.
Low becomes half low, second shows up at first and a half, etc.

So far so good. Then you have the problem of turning more RPM on the highway, thus using more gas... So you get more power, more usable torque, less mileage.

Now the new problem.
To maximize emissions per mile, and to increase the EPA and CAFE mileage numbers, they over-gear the trucks from the factory. They already have 'freeway' gears in them. 3.55 on a truck is very high (lower number) geared. Tall gears, another expression, help that cruise gas mileage and emissions.

Here is the sucky part. As the gears are so high, around town, you lug and struggle up to speed. It's a 6000 lb beast, and you are driving around like a ten speed stuck in high range. This is not good for gas mileage.

Everybody’s trucks are this way, unless you jump to Superduty types. Why? Different set of laws, emissions, etc. on the big trucks. Also, different mission. Few drive them just to be driving a truck. Well, more than a few, but not like drive half tons.

So it's normal for a one of these trucks with SLIGHTLY lower rear gears to get a little better mileage around town, and a little worse mileage on the freeway.

If you only have one gear set, it MIGHT pay to change to lower gear (higher number) if you 80% at least, drive around town. It would be possible that you do not get any gain. This is a crapshoot. Half the time you drive a little quicker, eating any possible gain.

Not gonna ever save enough gas to justify doing two rear ends. NOPE.
Guys like me with the small 8.8 open could make it pay for itself, as the job only costs about 400-500 bucks. But not in three or four years of normal driving.
Fuggedaboutit.
Lower gears are to compensate for big tires, or to make it quicker.
Chris

 

BRAVO Chris!!

couldn't have said it better myself. we used to race quarter mile alot in my old stang, swapping out 3:27 gears for 3:73 made a HUGE difference in 1/4 mile. Highway, sucked big time. Revved out in 5th gear like a lunatic.

Let's not forget how much of gas mileage comes down to driving style as well. Ham foot drivers, lunging off the line, kill mileage. The slow and steady, although annoying to people behind you, obviously yields better. However, you're driving style is subjective, where you may think you are easy going but aren't really when compared to others.

Enough Freudian stuff for tonite, enjoy!