My 03 Ex, 4.6l has the 3.73 LS gears. I don't know that much about gearing and was wondering if there is a better ratio for highway driving (which i do alot) for mpg's.

Any thoughts?

 

3.73 are fairly "short" gears, meaning the driveshaft spins 3.73 times for every 1 revolution of the rear axle. That's good for towing and acceleration, but at highway cruising it requires the motor to spin faster for the same speed(less MPG). Think of it as riding a bicycle in a low gear.

3.08 or 2.73 are "tall" or "highway" gears. It gives less torque and will dramatically reduce your tow capacity but give better MPG's on the highway, and the highway only. Around town the motor will have to work harder to accelerate and consume more gas in doing so, so any gains will be negated, like having to start off on a bicycle set to a high gear.

You can swap gears, but it's a fairly involved job and won't be cheap, several hundred at the absolute minimum DIY. Installed could near a thousand.

Plus, if it's 4wd that opens up a whole new can 'o worms. Either never use 4wd again, or you have to change the front axle as well. Otherwise POP! goes the t-case.

 

The short answer is the gear that allows the least throttle opeing to move the truck at satifactory speeds.
Your 3.73 rear gear results in a final drive ratio of 2.87 in over drive.
Using a 4r70w as an example; an AOD is somewhat a different OD ratio of .67.
That's 3.73 x .77= 2.8721.
This is why there is not much throttle response without gear kickdown in these heavey trucks.
Going to 3.55 x .77 = 2.7335 worse yet.
You have to make a decision because the lower numerically you go in final ratio the more throttle you need to make the motor power to keep the truck going and that in it'self causes higher fuel consumption hence the reason for the 'short answer' on the first line being a compromise.

 

My first Expy had a 4.6 with 3.55 gears and was a dog. It would get pretty good mileage cruising at 65 mph for 100 miles or more. But any steep grade or bad headwind and there goes the fuel. My 03 was the same as your vehicle and I was glad to have the 3.73 gears. The way Ford tunes the PCM, I don't think you will seem much improvement if you went to a 3.55. Maybe on a good day with a flat road and a tail wind you might get an additional 1 mpg.

Maybe if you are running at speeds in the 80-85 range and travel on an open road for 30 miles or more, the 3.55's may help. Any hills or head winds would cause the engine to have to work harder and would wipeout any benefit to the change in gearing. Otherwise, the 3.73 is the best gear for the heavy Expy.

If you have the time, drop your cruising speed by 5 mph and see the difference. Even a drop of 1 mph on a daily basis makes a difference with these trucks.

Good luck.

 

Great infor Blue Grass. Turns out I am actually running a 3.08 rear end!
I am a little dissapointed, but explains why she cant tow worth a crap. I have the 4.6L in a super/extended cab sonfiguration. I have decided to change up to a 3.73. I drove from texas to Virginia this past november with wife and son and a few hundred pounds of gear. The truck avgd 16.9mpg at 70 with or without a/c I was really impressed. Equally the only time I had the over drive off was driving the smokey mountain prkwy down from tenesse through N. Carolina. Other wise she stayed in over drive even on moderate grades. Ths was before my exhaust. I can still stay in over drive on the freeway with minimal headwind.
I think the 3.73s are going to be great!

 

The cost recoup time for the 1 mpg you might gain on the hwy is not worth it IMO. Also note that city MPG may go down due to increased effort of accelerating the truck, negating some of the benefit.

Assuming 17inch tires and a 3.73 is a good all around combo IMO. Your hwy rpms should be pretty low with the OD of these trannys.

 

IMO, 3.73 gears are one of the best with stock wheels/tires (or close) for overall MPG. It's a good blend for city and freeway driving. If your only reason to consider change is for MPG, it is definitely, 100% NOT worth it.

 

3.73 is probably the best overall ratio for a 4.6L on stock tires, if you have 20 inch, or larger equiv. you might want to consider 3.90s or 4.10s. The 4.6L lacks the low end torque to give decent city mpg, and is cruising at 65 below peak efficiency(as Bluegrass explained), which explains why many people can put 4.10s on stock tires and see no mileage drop.

I also have a 4.6L on stock tires, I currently have the 3.55LS and I am switching to the 4.10s (they're in my bedroom right now) for better city mileage and the added grunt for towing. I routinely tow arounds 4500 lbs. in areas with a 5-7% grade, and the truck cannot start from a stop that well on that kind of grade, it feels like I am flooring my Volkswagen (73 bug) with that kind of load.

Keep in mind however that any money spent to get taller (or shorter) gears is money that could've been spent on gas anyways, unless you plan on keeping that truck for a long time (100K or more) , I would rethink spending $500 for the sole purpose of fuel economy. Stop and think a second about what exactly you do with your truck on a regular basis, that should be your primary concern, if you do little or no towing, then a gear swap is 100% not worth it for you.

 

I have a 2000 4.6L F150 with the vagina 3.08 rear end. On the hwy I can get close to 20MPG with out head wind and minimal grades, however when you get above a 3% grade, it goes out of overdrive.
I have a drop in K&N filter, JBA 3.5" Single Out Exhaust, Hypertech 87 tuning, and all new cats and plugs, and 265/75/r16s (29" tires).
Around town I struggle to get 13 or 14. It SUCKS!
I was pndering 3.73's, but I think 4.10's are it for me. This 5400lb. beast needs all the torque she can get. I have been posting elsewhere and the guys seem to feel that there is little change in gas mileage with shorter gears.

 

3.30's with a 4.6 swb reg cab. Its a total dog and it gets about 16mpg in exclusive city driving. 4.88's are going in pretty soon.

 

i agree with bluegrass. i dropped down from 70 to around 60 on the highway and im averaging 16-18 mpg. also went 1 pound over on tire pressure. seemed to help. 16 mpg in city driving isnt that bad.

 

I get very good mileage with 3.55s in a Screw with the 5.4. High 16s to 17 around DFW and 19.2 on the highway. I don't baby it either, usuall 75 to 80 on the highway. The nice thing, it sets at 2000 rpms at 75.

 

Yeah, i can't complain about the 16mpg in the city, sure is slow though.

 

not with the EDGE!