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This is the closest I have, found that running 82 I got 4mpg better than 85 and with a 120 mile daily commute
it makes a difference.
Keeping the RPM in the sweet spot is the key. It looks like you're cruising along at 1,800 RPM.

If I'm towing at 65 mph with 3.92 gears, I'm also in the sweet spot, and pretty close to peak torque. If not towing, 3.22 gears is the way to go. If towing, the 3.92 is the way to go. The question remains, how much towing does most EcoDiesel owners actually do? Is 3.92 really worth it?

I do a lot of driving in the Rocky Mountain region, so that makes the 3.92s valuable even when unloaded (less downshifting). For me, the 3.92 is an easy decision. If I lived in the Midwest, it might be a tougher decision.
 

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Keeping the RPM in the sweet spot is the key. It looks like you're cruising along at 1,800 RPM.

If I'm towing at 65 mph with 3.92 gears, I'm also in the sweet spot, and pretty close to peak torque. If not towing, 3.22 gears is the way to go. If towing, the 3.92 is the way to go. The question remains, how much towing does most EcoDiesel owners actually do? Is 3.92 really worth it?

I do a lot of driving in the Rocky Mountain region, so that makes the 3.92s valuable even when unloaded (less downshifting). For me, the 3.92 is an easy decision. If I lived in the Midwest, it might be a tougher decision.
What is considered the sweet spot for towing? How accurate are our tachometers/speedometers in the trucks? I tow mostly at 65 mph. With 3.55 gears it runs 1/4-1/3 of the way between 2000-2250 rpm so pretty close to 2100 rpm. At 70 it runs 2250 almost dead on (in 7th gear) In 6th gear it runs 2250 ish at 60 mph and 2500 ish at 65 mph.

For the folks with 3.92's what rpm do you run at xyz speed? I do not tow in the mountains and rarely does the truck down shift from 7th, but i dont tow with the cruise on often and Id rather loose 5 mph by the crest of the hill then force a labored downshift.
 

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What is considered the sweet spot for towing?
There are 3 sweet spots with 3.92 gears for towing. They are listed below:
0-30 mph
39-47 mph
58-70 mph

Keep in mind, we are talking about the 3rd gen engine (480 lb-ft of peak torque @ 1,600 rpm).
 

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I tow mostly at 65 mph. With 3.55 gears it runs 1/4-1/3 of the way between 2000-2250 rpm so pretty close to 2100 rpm. At 70 it runs 2250 almost dead on (in 7th gear) In 6th gear it runs 2250 ish at 60 mph and 2500 ish at 65 mph.
MAS, you have the GDE EPA Compliant Tune, right? The max torque is 455 lb-ft @ 2540 RPM, but you're able to maintain close to max torque through 2,150 - 2,650 RPM. If I'm towing heavy, I lockout 7th gear. My 2015 also has 3.55 gears.

ProductionHot Tune
217 hp @ 3550 rpm250 hp @ 3550 rpm
405 lb-ft @ 2000 rpm455 lb-ft @ 2540 rpm


 

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Keep in mind, we are talking about the 3rd gen engine (480 lb-ft of peak torque @ 1,600 rpm).
Also GDE's figures are at the wheels numbers, so if you figure that you loose 9% on hp and 4% on torque roughly what GDE's figures show for advertised HP and at wheels power of the stock tune and apply that to the new gen motor. Puts the Gen 2 tuned and the Gen 3 very close performance wise.
 

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Also GDE's figures are at the wheels numbers, so if you figure that you loose 9% on hp and 4% on torque roughly what GDE's figures show for advertised HP and at wheels power of the stock tune and apply that to the new gen motor. Puts the Gen 2 tuned and the Gen 3 very close performance wise.
It will be interesting to see the horsepower/torque numbers that GDE comes up with on the dyno. My Gen 3 stock tune feels almost as good as my GDE tuned Gen 2 engine. We'll see how much tuning improvements can be made with the Gen 3 tuning.
 
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There are 3 sweet spots with 3.92 gears for towing. They are listed below:
0-30 mph
39-47 mph
58-70 mph
I know it's a discussion with no one answer, but I disagree with the 58-70 MPH point. The 3.21s have virtually identical HP and torque, just run one gear lower. I know the 3.92s pull better from a stop. I'm not sure about the 39-47 area. Did that value come from the other forum which was directed at gassers? From 2nd to 5th gear, 3.21s have more pull than 3.92s running one gear higher, so I don't see why the latter would have an advantage in the mid-range speeds. I would consider 8th a bonus OD for the 3.21 truck, although I sometimes use it on mild downhills (3.55s, FWIW) when towing.

As far as looking at peak torque, we know that the engines pull stronger somewhere up towards peak HP--and no, I don't understand why. I can tow up hills at 3,000 RPM where I would be losing speed at 2,400 RPM. I think my Gen 2 ED has peak torque at 1800, but I'm rarely that low when towing except on milder downhills.
 

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I disagree with the 58-70 MPH point.
The exact speeds may not be accurate, but the same principal applies. You acknowledged that someone with 3.21 gears will be running one gear lower just to maintain the same acceleration as the person towing with 3.92 gears. In other words, the person with 3.21 gears might not be able to maintain towing speeds near max load.

As highway speeds, the 2015 EcoDiesel with 3.92 gears is going to downshift less and maintain speed better than the 2015 EcoDiesel with 3.55 gears. Now, imagine the difference between 3.92 and 3.22 gears.

I think my Gen 2 ED has peak torque at 1800, but I'm rarely that low when towing except on milder downhills.
2014 - 2019 EcoDiesel
240 HP @ 3,600 RPM
420 LB-FT @ 2,000 RPM

2020 - Present EcoDiesel
260 HP @ 3,600 RPM
480 LB-FT @ 1,600 RPM
 

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The exact speeds may not be accurate, but the same principal applies. You acknowledged that someone with 3.21 gears will be running one gear lower just to maintain the same acceleration as the person towing with 3.92 gears. In other words, the person with 3.21 gears might not be able to maintain towing speeds near max load.

As highway speeds, the 2015 EcoDiesel with 3.92 gears is going to downshift less and maintain speed better than the 2015 EcoDiesel with 3.55 gears. Now, imagine the difference between 3.92 and 3.22 gears.
Why couldn't you "maintain towing speeds near max load" with virtually the same overall gear ratio, RPMs, torque, and HP? You wouldn't know the difference if you didn't check what gear it was in.

The 3.55s are in between, so there are speeds where it would be one gear lower than the 3.92s, but with higher RPMS and power, then it might want to shift a little sooner and have lower RPMs and power. Therefore, I might choose to cruise at a little different speed to keep in a comfortable RPM range. Accelerating, I would keep in a gear a little longer than the 3.92s, but not as long as the 3.21s. I wouldn't let it shift to a gear it was having trouble pulling.

I just realized I forgot to include a graph in my previous post that helped to show the comparison. I'm on a different computer, but I'll try to recreate it and add it.
 

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The 3.92s can pull stronger off the line and keep more RPMs crawling on dirt roads, but, once moving, the 3.21s can stay in a lower gear and actually have more pull at a given speed in gears 2-5 than 3.92s one gear higher. Gears 6 and 7 are virtually identical to 7 and 8 with the 3.92s.
Gear ratio comparisons.jpg
 

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Why couldn't you "maintain towing speeds near max load" with virtually the same overall gear ratio, RPMs, torque, and HP? You wouldn't know the difference if you didn't check what gear it was in.
You could maintain towing speeds if it was "virtually the same overall gear ratio", but it's not. Not even close. The person with 3.21 gears is gaining an overdrive gear but losing a towing gear. Here's the math that was presented in that thread:

From the speed 0-30 MPH, 3.92 has higher final drive ratio over 3.21 (18.46 vs 15.12) until it has to shift to 2nd gear at 30MPH.

From the speed 31-38 MPH, 3.21 has higher final drive ratio over 3.92 (15.12 vs 12.31) until it has to shift to 2nd gear at 38MPH.

From the speed 39-47 MPH, 3.92 has higher final drive ratio over 3.21 (12.31 vs 10.10) until it has to shift to 3rd gear at 47 MPH.

From the speed 48-57 MPH, 3.21 has higher final drive ratio over 3.92 (10.10 vs 8.23) until it has to shift to 3rd gear at 57 MPH.

From the speed 58-70 MPH, 3.92 has higher final drive ratio over 3.21 (8.23 vs 6.74) until it has to shift to 4th gear at 70 MPH.

"The key takeaway here is that towing heavier trailers uphill with 3.21 might never reach the desired speed within the 58-70 MPH range (typical highway towing speed) because 3.21 jumps from 10.10 to 6.74 without the 8.23 final drive ratio found in 3.92 that really help maintaining highway towing speed at max load."
 
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You could maintain towing speeds if it was "virtually the same overall gear ratio", but it's not. Not even close. The person with 3.21 gears is gaining an overdrive gear but losing a towing gear. Here's the math that was presented in that thread:

From the speed 0-30 MPH, 3.92 has higher final drive ratio over 3.21 (18.46 vs 15.12) until it has to shift to 2nd gear at 30MPH.

From the speed 31-38 MPH, 3.21 has higher final drive ratio over 3.92 (15.12 vs 12.31) until it has to shift to 2nd gear at 38MPH.

From the speed 39-47 MPH, 3.92 has higher final drive ratio over 3.21 (12.31 vs 10.10) until it has to shift to 3rd gear at 47 MPH.

From the speed 48-57 MPH, 3.21 has higher final drive ratio over 3.92 (10.10 vs 8.23) until it has to shift to 3rd gear at 57 MPH.

From the speed 58-70 MPH, 3.92 has higher final drive ratio over 3.21 (8.23 vs 6.74) until it has to shift to 4th gear at 70 MPH.

"The key takeaway here is that towing heavier trailers uphill with 3.21 might never reach the desired speed within the 58-70 MPH range (typical highway towing speed) because 3.21 jumps from 10.10 to 6.74 without the 8.23 final drive ratio found in 3.92 that really help maintaining highway towing speed at max load."
Firstly, he meant LOWER ratio when he said "higher". Secondly, he's talking about gassers that don't have the torque of our EDs. Notice he's talking about shifting into 4th at 70 MPH. Was he referring to shifting at 4,000 or 4,700 RPM? The RPM drops on an upshift are the same no matter which rear-end you have, so if you can make the shift with one, you can make it with the other--you just shift at a different speed.

I wish I had a program to graph RPMs vs speed for the different rear-ends. Perhaps someone here has seen such a graph they could share here.
 

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I modified an earlier post for first time readers but for the rest unless you look back you would never see it. So

At a max tow say its 8k the 3.21 has to divide the work IE accelerate the load up grades and on switchbacks up & down and or maintain interstate speed especially into the wind with one less gear.

Think carrying heavy shingles up two ladders to the roof of a house. One ladder has 5 big steps one has 4 giant steps. The ladder steps represent the gears the 3.21 & 3.92 has available to use ie has enough torque or is strong enough to use when towing this load.

It's much harder and slower to carry the shingles to the top with 4 steps. Now you are on the roof turn the corner you have 40 more ladders or switchbacks to do to get to the top roof or crest the mountain.

Are you picking 4 step ladders or 5 step ladders on your path to the top? 5 right because its easier and faster if you are carrying a heavy bundle of shingles. I mean If you are not carrying any shingles you might for speed choose the 4 step ladders to the top. Anyway now you are at the top. Which ladder path made you sweat the most or overhead first on the way up? The 4 step ladders right? Which ladder set made you use the most energy or fuel to get to the top? The 4 step ladders right? Don't set down the shingles you have to carry them back to the ground. Are you going to choose the 4 step or 5 step ladders to control your descent to the ground?

This represents one hill or mountain. The west if full of mountains.

Even with just 3.55 vs 3.92 we have often read on here over the years that 3.55 "holds the line" at 45 mph and the 3.92 at 50 mph.
 

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Fortunately our trucks and 8 speed transmissions are better at working their azz off than we are… at least most of them are… trucks did this back in the day with less horsepower less torque and only a 2 or 3 step ladder as we are describing it.
 

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Secondly, he's talking about gassers that don't have the torque of our EDs.
The speed and shift range will vary between the engines offered in the same platform. But we aren't comparing the Hemi to the Ecodiesel. We are comparing gears. Whether you're driving an EcoDiesel, Pentastar, or Hemi, the 3.92 gears will always outperform 3.21 gears when towing at highway speeds, especially near max tow and/or in mountainous terrain. There's a reason why the tow rating is increased with 3.92 gears. Tow capacities are based on the SAE J2807 towing test. The 3.21 gears have a lower towing capacity because they can't perform as well as the 3.92 gears. It could be due to a lack of speed, or a lack of engine cooling, or a combination of the two.
 

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Tow capacities are based on the SAE J2807 towing test. The 3.21 gears have a lower towing capacity because they can't perform as well as the 3.92 gears. It could be due to a lack of speed, or a lack of engine cooling, or a combination of the two.
Several of the testing cycles of the J2807 are time based. The truck has to be able to get the load moving to a certain speed or distance repeatedly within a specified time frame.
 

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Several of the testing cycles of the J2807 are time based. The truck has to be able to get the load moving to a certain speed or distance repeatedly within a specified time frame.
Correct. What I believe you're referring to is the "Launch on Grade Test".

"To pass, while on an incredibly steep 12 percent grade, a truck must be able to launch and travel 16 feet (5 meters) uphill, five times in a row, in 5 minutes or less. Then, the truck and trailer has to be able to complete the same test while launching up a 12 percent grade in Reverse."

There's also the "Flat-Out Acceleration Test" which measures the passing capability of the truck/trailer combination.

The "Highway Gradeability Test" climbs 3,500'+ feet over 11.4 miles. It really challenges the capability the truck. The ambient temperature must be a minimum of 100*F at the base. The A/C has to be turned on and the blower fan at full blast. To pass this test, the truck/trailer combination must maintain a minimum of 40 mph and throw no codes.

The 2014 - 2019 Ram 1500 Hemi actually outperformed the Ram 1500 EcoDiesel on the gradeability test due to cooling restrictions of the EcoDisesel. That's why the Hemi has a higher towing capacity than the EcoDiesel.
 

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Correct. What I believe you're referring to is the "Launch on Grade Test".

"To pass, while on an incredibly steep 12 percent grade, a truck must be able to launch and travel 16 feet (5 meters) uphill, five times in a row, in 5 minutes or less. Then, the truck and trailer has to be able to complete the same test while launching up a 12 percent grade in Reverse."

There's also the "Flat-Out Acceleration Test" which measures the passing capability of the truck/trailer combination.

The "Highway Gradeability Test" climbs 3,500'+ feet over 11.4 miles. It really challenges the capability the truck. The ambient temperature must be a minimum of 100*F at the base. The A/C has to be turned on and the blower fan at full blast. To pass this test, the truck/trailer combination must maintain a minimum of 40 mph and throw no codes.

The 2014 - 2019 Ram 1500 Hemi actually outperformed the Ram 1500 EcoDiesel on the gradeability test due to cooling restrictions of the EcoDisesel. That's why the Hemi has a higher towing capacity than the EcoDiesel.
That makes perfect sense. The 3.92s have an unquestioned advantage getting a heavy load moving in first gear, and a little advantage in the next couple of gears.

I have yet to see anyone explain how "the 3.92 gears will always outperform 3.21 gears when towing at highway speeds" when they give virtually identical ratio choices, albeit in one gear higher. For example, 3.21s in 6th gear at 2,400 RPM would be going the same speed as 3.92s in 7th gear at 2,462 RPM. One gear higher, the 3.21s would be at 2,464 and 3.92s at 2,400.
 

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That makes perfect sense. The 3.92s have an unquestioned advantage getting a heavy load moving in first gear, and a little advantage in the next couple of gears.

I have yet to see anyone explain how "the 3.92 gears will always outperform 3.21 gears when towing at highway speeds" when they give virtually identical ratio choices, albeit in one gear higher. For example, 3.21s in 6th gear at 2,400 RPM would be going the same speed as 3.92s in 7th gear at 2,462 RPM. One gear higher, the 3.21s would be at 2,464 and 3.92s at 2,400.
Actually, real-world testing (and personal experience) shows the opposite. There's very little difference between 3.21 and 3.92 when doing the 0 - 60 test or 1/4 mile testing. The real difference is when you take a trailer (at max load) over a mountain pass. The 3.21 can't maintain speed, not even in a lower gear. I've literally had my 2015 (with 3.55 gears) slow down to 28 mph on a long steep grade. Why? Because the truck can't maintain speed, so I end up in a non-towing gear and the truck feels gutless. This is why the 3.92 EcoDiesel is rated to tow more than the 3.21 EcoDiesel.

SlowRoller, it doesn't sound like you're towing near maximum capacity and/or towing on long steep grades, so you might not have major cooling issues. If you run into cooling issues, there are three things that you can do to help.
1. Change to the honeycomb style grille if you have one of the restrictive grilles.
2. GDE offers a lower temperature thermostat that reduces coolant and oil temps about 18*F.
3. Tune

The 2020+ 3rd gen EcoDiesel DOES NOT have a cooling issue, which is why it's towing capacity is more closely rated to the Hemi etorque.
 

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Actually, real-world testing (and personal experience) shows the opposite. There's very little difference between 3.21 and 3.92 when doing the 0 - 60 test or 1/4 mile testing. The real difference is when you take a trailer (at max load) over a mountain pass. The 3.21 can't maintain speed, not even in a lower gear. I've literally had my 2015 (with 3.55 gears) slow down to 28 mph on a long steep grade. Why? Because the truck can't maintain speed, so I end up in a non-towing gear and the truck feels gutless. This is why the 3.92 EcoDiesel is rated to tow more than the 3.21 EcoDiesel.

SlowRoller, it doesn't sound like you're towing near maximum capacity and/or towing on long steep grades, so you might not have major cooling issues. If you run into cooling issues, there are three things that you can do to help.
1. Change to the honeycomb style grille if you have one of the restrictive grilles.
2. GDE offers a lower temperature thermostat that reduces coolant and oil temps about 18*F.
3. Tune

The 2020+ 3rd gen EcoDiesel DOES NOT have a cooling issue, which is why it's towing capacity is more closely rated to the Hemi etorque.
I have the 3.92 on my 2015
wouldnt have anything else
live inutah hills mountains etc
drive a lot of dirt roads steep rough slow have e rated tires
more than happy
if there’s a difference in mileage it’s overridden by the safety and satisfaction of the ratio and tired
 
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