packplantpath

Just made the first tow today with my 4x4 eco with 3.31. 2 round bales of hay on a old heavy dual axle trailer. Figure 4000 lbs.

Very light but it had plenty of pep and pulled smooth.

Mike Up

Just so you know, the 3.31 gear takes away much of the Ecoboosts advantage over a 5.0L with 3.73 gears.

Using the 3.55 gears as a standard which torque and horsepower are referenced with, here's a break down.





A 3.31 gear is 6.8% larger than a 3.55 gear meaning a loss of 6.8% torque.

A 3.73 gear is 5.1% smaller than a 3.55 gear meaning a gain of 5.1% torque.

Horsepower formula is Torque * rpm/ 5252 = HP

Ecoboost has 365 horsepower at 5000 rpms (referenced to a 3.55 standard axle). The Ecoboost has about 387 lbs of torque at 5000 rpms. With a loss of 6.8%. 6.8% * 387 = 26.316 . 387 - 26.316 = 360.684 (~361 lbs of torque). 361 lbs * 5000 = 1805000 . 1805000/5252 = 343.678 HP (344 HP). You've lost 21 horsepower with a 3.31 gear on your ecoboost.

5.0L has 363 lbs of torque at 5000 rpm. 363 lbs * 5.1% = 18.5 lbs . 363 lbs + ~19 lbs = 382 lbs. 382 * 5000 rpms = 1910000 . 1910000/5252 = 363.67 HP (364 HP).

So at 5000 rpms, the 5.0L will have 20 HP more than an Ecoboost. The lower rpm is still good but marginally better than the 5.0L and looses a lot at higher rpms.

So by getting the 3.31 option with the Ecoboost, you really lose the main benefit of the Ecoboost, and that's power. The mpg is about equal between the two so the power is the large benefit of the Ecoboost.

So if you have any choice at all, avoid the 3.31 gears.

Brianstemm

My understanding is horsepower is what it is, gearing just determines how the transmission uses it. I'm not sure you percentile calculations are translated accurately.

TommyB80

I regret mine with the 3.31's. Towing an aluminum trailer with 2 utility quads it gets 10mpg. If I could have done it over I would have gotten the 3.73's or at least 3.55's. Otherwise I like the truck.

Mike Up

You have it wrong. Horsepower is based off of torque with the formula (Torque * RPM) / 5252 .

I used Ford's base torque ratings based on a 3.55 axle. With a 3.31 axle, you will lose torque, and with a 3.73 axle, you will gain it. A 3.31 may help with fuel economy at highway speeds with NO LOAD but you lose power.

Axle gears are torque multipliers. The Ford torque charts are from the flywheel with no torque multiplier yet.

Not all torque multipliers/dividers are taken in account, as the transmission gears, wheel size, or driveline loss. Just simplifying it with flywheel torque and axle gears (3.55 being the reference used for the base torque).

The ford charts aren't an end all as driveline loss isn't factored in, wheel size, transmission gears or axle gearing.

I was just making a comparison to show the dramatic loss of going with a 3.31 axle.

If you were soley buying the Ecoboost for power output but decided on a 3.31, you may as well go for a cheaper 5.0L with the 3.73 because your torque won't be far behind and you will have more available horespower.

packplantpath

Mike my only complaint about the comparison is you are using peak numbers. The benefit of the eco is the flat torque curve. Yes, the 3.31 utilizes it less effectively but the flat curve still provides a benefit over the 5.0 even with 3.31s. Especially with computer controlled shift adjustments in tow/haul mode.

In the real world, peak numbers at 5000 rpm are not really useful.

Mike Up

That peak of 5000 is only for the Eco so it's not peak for the 5.0L. The 5.0L will have even more power at it's peak of 5500 rpms. 350 lbs * 5.1% = 17.85+ 350 = 367.85 lbs (~368 lbs ). 368 lbs * 5500 rpms = 2024000 . 2024000/5252 = 385.37 HP (385 HP). So the 5.0L with 3.73 axle would have a geared 385 Hp, the Ecoboost with 3.31 axle would have a geared 344 Hp. That's a geared 41 Hp difference, HUGE.

The moral of the story is don't go with the 3.31 if you're after power. The Eco has so much torque, you may only need the 3.55 axle. But if you're power hungry and don't care about highway mileage, get the FX4 Ecoboost with the optional 4.10 axle and get power out the ****!!

Gearing is such a huge difference that nobody considers the transmission gearing or the axle gearing. All they look at is the engine rating and consider nothing else. That's why a Dodge Ram 390 HP Hemi 5.7L Crew Cab 4WD truck has the exact same 0 - 60 mph and 1/4 mile time as a Ford F150 360 HP 5.0L F150 Crew Cab 4WD truck. Dodges 5 and 6 speed transmissions suck with a low 3.00:1 1st gear. The rest of the gear are also taller creating less torque than the awesome Ford 6 speed transmission gearing.

I drove a 2008 F150 Screw 5.4L w/3.73 axle and it's crappy 4 speed transmission. It felt like a dog. I bought my 2010 F150 Screw 5.4L w/355 axle and it's awesome 6 speed transmission (geared LOW), and it felt like another 60 Hp and torque. The 2010 proved it provided much more power as it had a 0 - 60 time at 1 second faster along with a much quicker 1/4 miles time.

The 2010 had tons more torque because of the geared torque multiplier in the new 6 speed transmission. 6 speed trans has a 1st gear of 4.17:1 while the 4 speed has a 1st gear of 2.84:1, A HUGE DIFFERENCE!

With engine power very close between trucks, the axle gearing and transmission can make more of a difference than just the engine.

MadocHandyman

It's not your ratio. I have 3:31's and tow a tall enclosed trailer, around 3500 lbs. On windy days in hilly areas, keeping up with and sometimes ahead of traffic, I get 13 mpg +. Nice calm days I've had as high as 17 mpg.

Mike Up

I do want to add though, even with the 3.31 axle, you'll still have more low end torque than a 5.0L with the 3.73, you'll just lose upper RPM horsepower. So why not get the full power of the Ecoboost and stick with the 3.55, 3.73, or 4.10 to get the most out of the engine, IF YOU CAN.

All referenced off of a base torque value with a 3.55 axle.


5.0L w/3.55 axle

1500 rpm = 275#

2000 rpm = 302#

2500 rpm = 315#

3000 rpm = 327#

3500 rpm = 350#

4000 rpm = 365#

4250 rpm = 380#

4500 rpm = 375#

5000 rpm = 363#

5500 rpm = 348#

6000 rpm = 315# (Redline)



5.0L w/3.73 axle

1500 rpm = 289#

2000 rpm = 317#

2500 rpm = 331#

3000 rpm = 343#

3500 rpm = 368#

4000 rpm = 383#

4250 rpm = 399#

4500 rpm = 394#

5000 rpm = 377#

5500 rpm = 365#

6000 rpm = 331# (Redline)



3.5L w/3.55 axle

1500 rpm = 375#

2000 rpm = 381#

2500 rpm = 420#

3000 rpm = 420#

3500 rpm = 413#

4000 rpm = 413#

4250 rpm = 402#

4500 rpm = 400#

5000 rpm = 388#

5500 rpm = 352#

6000 rpm = 275# (Redline)



3.5L w/3.31 axle

1500 rpm = 350#

2000 rpm = 355#

2500 rpm = 392#

3000 rpm = 392#

3500 rpm = 385#

4000 rpm = 385#

4250 rpm = 375#

4500 rpm = 373#

5000 rpm = 362#

5500 rpm = 328#

6000 rpm = 256# (Redline)



5.0L w/3.73 axle compared to 3.5L w/ 3.31 axle

1500 rpm = -61#

2000 rpm = -38#

2500 rpm = -61#

3000 rpm = -49#

3500 rpm = -17#

4000 rpm = -2#

4250 rpm = +24#

4500 rpm = +21#

5000 rpm = +15#

5500 rpm = +37#

6000 rpm = +75# (Redline)

MadocHandyman

I think what packplant might be getting at is with the torque of the Eco coupled with 6 speed trans, you won't notice a reduction in torque or HP until 6th gear.
So as soon as it needs the added torque, it just drops a gear. The engine will still put out the same power, just requires a different gear to use it.
Am I close?