3.92 with the Ecodiesel

[Willwork4truck]

I have 3.92 and it runs great. added 35s lift and camper shell (weight) and the truck runs no different than stock.

Its accurate to say the 3.92’s are basically necessary (hemi or diesel) if you have a lift and bigger wheels, 35’s, 37’s especially, as well as a truck camper. If like me you only plan on getting some taller profile 22’s and don’t tow/carry a camper then likely not.

 

[Zoompastu]

Just an FYI the gear ratios that were posted in that chart are no longer accurate either.... We have minor gear ratio changes with the new 8HP75 transmission
4thGen / 5th Gen
8HP70 / 8HP75
First – 4.71/ 5.00
Second – 3.14/ 3.20
Third – 2.10/ 2.14
Fourth – 1.66/ 1.72
Fifth – 1.28/ 1.31
Sixth – 1.00/ 1.00
Seventh – 0.83/ 0.82
Eighth – 0.66/ 0.64
Reverse – 3.30/ 3.45

 

[silver billet]

Just an FYI the gear ratios that were posted in that chart are no longer accurate either.... We have minor gear ratio changes with the new 8HP75 transmission
4thGen / 5th Gen
8HP70 / 8HP75
First – 4.71/ 5.00
Second – 3.14/ 3.20
Third – 2.10/ 2.14
Fourth – 1.66/ 1.72
Fifth – 1.28/ 1.31
Sixth – 1.00/ 1.00
Seventh – 0.83/ 0.82
Eighth – 0.66/ 0.64
Reverse – 3.30/ 3.45

Thanks for correcting me on that. I added the 8HP75 to the bottom of the chart. Interesting that one of the overlapping gear differences grows a bit more so I removed it as "equal", but 6 and 7 are now pretty much "really really equal".

I think the point remains. Once both transmissions are at 3'rd and beyond, the pulling power advantage of the 3.92 is reduced to almost nothing, and the mpg advantage of the 3.21 is increased, since it basically gets an additional top gear.

 

[Willwork4truck]

Just an FYI the gear ratios that were posted in that chart are no longer accurate either.... We have minor gear ratio changes with the new 8HP75 transmission
4thGen / 5th Gen
8HP70 / 8HP75
First – 4.71/ 5.00
Second – 3.14/ 3.20
Third – 2.10/ 2.14
Fourth – 1.66/ 1.72
Fifth – 1.28/ 1.31
Sixth – 1.00/ 1.00
Seventh – 0.83/ 0.82
Eighth – 0.66/ 0.64
Reverse – 3.30/ 3.45

Thanks for the update, and that’s a great screen name!

 

[StuartV]

Which requires more fuel: maintaining speed on the interstate, or getting a 5,500 lb. vehicle moving from a stop?

I posted this in another thread which took some time, so I won't do it here, but there are NO points in any gear where the RPM overlaps between 3.21 and 3.92 axle gears in these trucks. The RPMs are different at any speed between the two, and not only does the 3.92 have to work less to get the truck moving which improves mileage around town, or with a trailer, or without a trailer, but it also responds better in the middle gears and it has an 8th gear RPM that's actually more comfortable on the highway, where the 3.21s would either put you at higher RPM in 7th or lower RPM in 8th and cause more downshifting.

There's a reason the 3.92 gears are an option that you pay for, and it's because they know it's the most desirable ratio.

How long is a piece of string? Your question has no answer.

The rest of what you said is pretty much wrong. But, I'm not going to spend the time now to post all the corrections. Suffice it to say that I have only owned 3.92 gears for the last 11 years, and I have driven my brother's virtually identical 1500 with 3.21 gears and, when unloaded/not towing, the take off is identical. It's limited by traction, not the torque being put to the ground.

 

[WXman]

How long is a piece of string? Your question has no answer.

The rest of what you said is pretty much wrong. But, I'm not going to spend the time now to post all the corrections. Suffice it to say that I have only owned 3.92 gears for the last 11 years, and I have driven my brother's virtually identical 1500 with 3.21 gears and, when unloaded/not towing, the take off is identical. It's limited by traction, not the torque being put to the ground.

In engineering, the question very much has an answer. Science tells us an object in motion tends to stay in motion. It requires more energy to get the truck moving and accelerate and that doesn't just apply to 1st gear. That's true until you reach terminal speed.

You can slice the watermelon however you want, but it's still a watermelon and the fact still remains that 3.92 axle ratio WILL get off the line with more ease, will accelerate with more ease, and will hold 8th gear more of the time on the interstate completely negating the assumed advantage of the 3.21s on the highway. Traction plays no role, since these 260 HP, 5,500 lb. pigs can hardly break the tires loose anyhow when combined with the turbo lag they produce.

I've had FCA vehicles with everything from 2.65 to 4.88 axle ratios. I've regeared cars, SUVs, and pickups in the garage. I have never found one single advantage to a numerically lower gear ratio. Then again, I don't live in Kansas where everything is flat and a mole hill is a mountain.

If you're running 80+ MPH you may see the 3.21s start to gain advantage. How many of us spend a majority of time above the speed limit on U.S. interstates?

 

[StuartV]

@WXman

I forget we're in the ED subforum. I take back what I said about being equal off the line. I was thinking of Hemis.

However, anywhere in between stopped and Interstate speeds, your statement that 3.92 "will accelerate with more ease" is just incorrect. It totally depends on specifics. A speed that has the 3.21-geared tranny in 2nd (or 3rd or 4th, etc.) gear and the sweet spot of RPMs will accelerate better than a 3.92 in 3rd gear at whatever RPM that works out to. Because that's what happens, right? When you're driving along at any of those intermediate speeds, the 2 will either be in the same gear or the 3.92 truck will be in a numerically higher gear. And when you're driving along with a 3.21 in 4th and a 3.92 in 5th, which one is going to accelerate with "more ease"?

Yes, the 3.92 will hold 8th more of the time than a 3.21. Duh. But, it is incorrect to say that that means it will get better mileage all of the time. With the torque curve of the ED, there will be plenty of scenarios where the fuel economy of lower RPMs will more than offset the times the 3.21 has to downshift.

I mean, you said you have never found ANY advantage to taller gearing. Did you even watch the video that was linked upthread? 4 MPG difference and that was, apparently, cruising at 70.

Personally, I NEVER go the speed limit. If you really do spend the majority of your time going the speed limit or less, you are definitely in the vast minority, as far as the drivers I see. My standard is 10 MPH over the speed limit at all times. And I am RARELY the fastest person on the road. Usually, I am just going with the flow of traffic. And that means I am going 80 almost any time I am on an Interstate.

To me, if you have any kind of real towing needs, get a 2500 with a Cummins. The 1500 with ED is for people who rack up miles and want better fuel economy. In which case, you're defeating the purpose if you get 3.92 gears.

I have averaged about 20 - 24,000 miles a year every year for the last 11 years, at least. Since I got my current truck, it's been 2,000 per month. I have had 3.92 gears and a Hemi for the last 11 years. But, I have learned my lesson (finally). My next truck will definitely have 3.21 gears. For those of us that don't do any significant towing, I can't see any advantage to 3.92 gears in the diesel other than take off response from a stop. And when I get an ED, I am very hopeful that GDE or somebody else will have a tuner for me that addresses that particular issue.

 

[silver billet]

@WXman

I forget we're in the ED subforum. I take back what I said about being equal off the line. I was thinking of Hemis.

However, anywhere in between stopped and Interstate speeds, your statement that 3.92 "will accelerate with more ease" is just incorrect. It totally depends on specifics. A speed that has the 3.21-geared tranny in 2nd (or 3rd or 4th, etc.) gear and the sweet spot of RPMs will accelerate better than a 3.92 in 3rd gear at whatever RPM that works out to. Because that's what happens, right? When you're driving along at any of those intermediate speeds, the 2 will either be in the same gear or the 3.92 truck will be in a numerically higher gear. And when you're driving along with a 3.21 in 4th and a 3.92 in 5th, which one is going to accelerate with "more ease"?

Yes, the 3.92 will hold 8th more of the time than a 3.21. Duh. But, it is incorrect to say that that means it will get better mileage all of the time. With the torque curve of the ED, there will be plenty of scenarios where the fuel economy of lower RPMs will more than offset the times the 3.21 has to downshift.

I mean, you said you have never found ANY advantage to taller gearing. Did you even watch the video that was linked upthread? 4 MPG difference and that was, apparently, cruising at 70.

Personally, I NEVER go the speed limit. If you really do spend the majority of your time going the speed limit or less, you are definitely in the vast minority, as far as the drivers I see. My standard is 10 MPH over the speed limit at all times. And I am RARELY the fastest person on the road. Usually, I am just going with the flow of traffic. And that means I am going 80 almost any time I am on an Interstate.

To me, if you have any kind of real towing needs, get a 2500 with a Cummins. The 1500 with ED is for people who rack up miles and want better fuel economy. In which case, you're defeating the purpose if you get 3.92 gears.

I have averaged about 20 - 24,000 miles a year every year for the last 11 years, at least. Since I got my current truck, it's been 2,000 per month. I have had 3.92 gears and a Hemi for the last 11 years. But, I have learned my lesson (finally). My next truck will definitely have 3.21 gears. For those of us that don't do any significant towing, I can't see any advantage to 3.92 gears in the diesel other than take off response from a stop. And when I get an ED, I am very hopeful that GDE or somebody else will have a tuner for me that addresses that particular issue.

I'm trying not to be a d__k, but he doesn't get this whole thing. I've explained it to him several times now, and he just ignores the posts or doesn't understand how to read the chart. But in any case, the chart makes it clear to me; the 3.92 in 8th, = the 3.21 in 7th; ie, they're going to have the same torque at same rpm and speed (within reason, they're not 100% identical but look at the difference, "0.12". And 3.92 in 7th vs 3.21 in 6th is even closer; equal to 100'th decimal place.

 

[Willwork4truck]

I’m not going to reread the multiple threads about 3.21 vs 3.92 that have been around since time began, I mean for a while, however I would think most agree that the deeper the gears that easier it is to get started, or it compensates for the loss of gearing due to installing taller tires. That’s pretty much the advantage. At higher speeds it just revs more.

Now an engineer might be trying to analyze at what speed the transmission is in the best torque curve range on whatever road/incline, but for most of us, the ZF takes care of that.

RAM offers us just two gear choices. iMHO they should have left us with the 3.55 as well. Then the pure grocery getters (like me) would have bought 3.21’s. The mid-range maybe tow, maybe not’s would have taken the 3.55 and the (old Ferd and GM crowd used to 4.10’s) tow-ers or ”I’m putting on 37’s” would likely have taken the 3.92. Not quite that clear cut but close.

Now we’ve got a fantastic 8 speed transmission that will accomplish pretty much anything unless you tow heavy, then take the 3.92 to help you down low/starting off. All IMHO of course, coming from the days of 3 speed auto’s where if you didn’t get a 4.10 you couldn’t pull your mother-in-law out of the front door.

 

[Aseras]

Or they could have a real engineer design a real overdrive gear the transmission uses for light cruising on the highway and use that when the engine isn't lugging and senses a load. Then they could easily have beaten the duramax an gotten better MPG all around across the board.

Cars had 3 and 4 gears for 50 years, we'd survive having a very tall final drive on a diesel to get better highway mileage and downshifting to 7th for towing.

 

[J-Cooz]

I’m not going to reread the multiple threads about 3.21 vs 3.92 that have been around since time bega, I mean for a while, however I would think most agree that the deeper the gears that easier it is to get started, or it compensates for the loss of gearing due to installing taller tires. That’s pretty much the advantage. At higher speeds it just revs more.

Now an engineer might be trying to analyze at what speed the transmission is in the best torque curve range on whatever road/incline, but for most of us, the ZF takes care of that.

RAM offers us just two gear choices. iMHO they should have left us with the 3.55 as well. Then the pure grocery getters (like me) would have bought 3.21’s. The mid-range maybe tow, maybe not’s would have taken the 3.55 and the (old Ferd and GM crowd used to 4.10’s) tow-ers or ”I’m putting on 37’s” would likely have taken the 3.92. Not quite that clear cut but close.

Now we’ve got a fantastic 8 speed transmission that will accomplish pretty much anything unless you tow heavy, then take the 3.92 to help you down low/starting off. All IMHO of course, coming from the days of 3 speed auto’s where if you didn’t get a 4.10 you couldn’t pull your mother-in-law out of the front door.

I believe there is a 3.55 option. I built a limited on the USA site with the EcoDiesel and it has the option, while the Canadian site doesn't. Seems odd.

 

[imolar]

I believe there is a 3.55 option. I built a limited on the USA site with the EcoDiesel and it has the option, while the Canadian site doesn't. Seems odd.

Hmm, pretty sure if you select the 3.55 it will take away the 3.0 option. I just did it to confirm and it definitely took away the EcoDiesel when I selected it.

 

[HST]

With 285 x 65 x20 tires i figure i am right around 3.64 for the rear end gear ratio , best of both worlds for me .

 

[1JK]

For those thinking about purchasing, I'm very pleased with my ED 3.92. getting 27, 28, 29 mpg, (23.5 avg for my mixed driving thru a MI winter) with a full size, great riding PU truck is awesome. For me, if I needed better milage than this I would'nt have purchased a truck.

 

[jdawgjm]

Thanks for correcting me on that. I added the 8HP75 to the bottom of the chart. Interesting that one of the overlapping gear differences grows a bit more so I removed it as "equal", but 6 and 7 are now pretty much "really really equal".

I think the point remains. Once both transmissions are at 3'rd and beyond, the pulling power advantage of the 3.92 is reduced to almost nothing, and the mpg advantage of the 3.21 is increased, since it basically gets an additional top gear.

View attachment 53518

This is really great

This is the kind of chart they need to post on the Dodge specs page.

 

[WXman]

Its accurate to say the 3.92’s are basically necessary (hemi or diesel) if you have a lift and bigger wheels, 35’s, 37’s especially, as well as a truck camper. If like me you only plan on getting some taller profile 22’s and don’t tow/carry a camper then likely not.

Yeah that's another good point. I'm about to put 295/70-18 tires on mine, which will effectively be like having a 3.65 axle ratio on the current tires. I expect to see a roughly 200 RPM decrease on the highway.

 

[joefriendly]

I ordered my 10th edition limited long horn 3.92 gears eco diesel. My second one, love these engines! Won't be here till March 2021 I have. 2014 ecodiesel ram long horn with 3.55 and it fine too, get 22 mileage per gallon all around driving, before recall got 25 miles per. And tows good, but half the fuel milage, which is good for towing. My friend has a 2016 eco diesel with 3.92 and love it's. say it's worth the less fuel miliage. I hope this new motor wholes up like last one? My EGR is still good on 2014, but there is a recall on it. It has 140,000 miles on it.

 

[mghurle]

I so very much regret not reading this forum until after my purchase. Last week, I purchased a 2021 Laramie Longhorn with the 3.0 EcoDiesel and 3.92 gearing. My trade in was a 2019 Ford F150 with the 3.0 PowerStroke V6. In my side job, I normally transport 20 bumper pull travel trailers annually, weighing between 5000-9000 pounds. My biggest complaint is HIGHWAY MILEAGE! I drive normally 80 with the cruise on going to pick up these trailers empty and averaged 25-27mpg with my Ford. Driving home the best I can get with the Ram is 21-22mpg. This figure alone has already got me looking to see when I can get out of the truck without loosing way too much money. Yes, I am quietly kicking myself for not reading about the difference of the 3.21 vs 3.92.

 

[Hrspwr88]

I couldn't build my ED with a 3.21. I tried, they told me it wasn't offered even after I was able to 'click' it while building it online. At the dealer, their build site wouldn't let them. I was hoping for highway mileage also...

 

[Neurobit]

I so very much regret not reading this forum until after my purchase. Last week, I purchased a 2021 Laramie Longhorn with the 3.0 EcoDiesel and 3.92 gearing. My trade in was a 2019 Ford F150 with the 3.0 PowerStroke V6. In my side job, I normally transport 20 bumper pull travel trailers annually, weighing between 5000-9000 ppunds. My biggest complaint is HIGHWAY MILEAGE! I drive normally 80 with the cruise on going to pick up these trailers empty and averaged 25-27mpg with my Ford. Driving home the best I can get with the Ram is 21mpg. This figure alone has already got me looking to see when I can get out of the truck without loosing way too much money. Yes, I am quietly kicking myself for not reading about the difference of the 3.21 vs 3.92.

Dang, that’s pretty, pretty low for an ED. For contrast, I average ~18-19MPG with my HEMI and 3.21 gearing (75-80 MPH).
That being said, it drops to 10 in city driving since my commute is stupid-short.

Curious. What kind of MPG are you getting around town though?