3.21 vs 3.92: The Last Word

[bigdodge]

Have you done the math?

What if the gear ratios in the tranny of an HD truck are taller than the 1500s? So that the actual final drive ratio of an HD with a 3.73 is the same as a half ton with a 3.21? Maybe an HD with 3.73 is already the same as a 1500 with 3.21.

A 1500 with 3.21 going down the highway at 80 MPH is turning about 1800 RPMs, I think (versus about 2200 RPMs with a 3.92). What RPMs is an HD with 3.73 turning at 80 MPH?

you are no fun

who wants to do math!!!

 

[Ninety-9 SE-L]

Mother of....here...

Yes, good job. You posted exactly the same data as I posted, but in a less useful way.

I sorted it the way I did so it can be interpreted the way the A/T's computer would utilize it. The AT only downshifts when it needs a particular amount of torque. Where the 3.92 might downshift into 4th, the 3.21 would downshift into 3rd, but overall, you'd have the same amount of torque coming off the wheels. This is why people keep mentioning that the 3.21 is simply a gear lower, but missing that first gear.

Well....yeah.

Again, selective hearing. Second part of my statement is important. What are you, the news media?

What do 35" tires do to the 3.21s?

Axle Ratio and Tire Size are one in the same. The same principal that gives the 3.21 a lower torque/speed ratio is what gives bigger tires a lower torque/speed ratio. More speed per rev also means less torque.
You're smart enough to know that, right?

Right, that's what I said. Theory and equations. They aren't good at dealing with what happens once their designs hit the real world. That's why people who are take over.

I'll remain rigid on the mechanics. In 'Theory' the Ram 1500 is many times more capable than as advertised, but we have to de-rate it because people like this exist:



Situational awareness is the best safety feature on your truck. But if you can't tow responsibly, I guess the 3.92 will solve all of your problems.

 

[SnowBlaZR2]

Yes, good job. You posted exactly the same data as I posted, but in a less useful way.

I sorted it the way I did so it can be interpreted the way the A/T's computer would utilize it. The AT only downshifts when it needs a particular amount of torque. Where the 3.92 might downshift into 4th, the 3.21 would downshift into 3rd, but overall, you'd have the same amount of torque coming off the wheels. This is why people keep mentioning that the 3.21 is simply a gear lower, but missing that first gear.

I made it more readable. In other words, more useful.

Depending on driving conditions and vehicle speed, there could be a 6-800 RPM or more difference between the two trucks at a given point in time. Considering shift points, mappings, and so on, I'm not sure why anyone who knows what they're talking about would claim that the two trucks would be the same except one would always be a gear lower. Do you have the shift mappings? Kind of makes me want to dust off HPT to take a look...

Again, selective hearing. Second part of my statement is important. What are you, the news media?

I isolated the part that actually matters...

Axle Ratio and Tire Size are one in the same. The same principal that gives the 3.21 a lower torque/speed ratio is what gives bigger tires a lower torque/speed ratio. More speed per rev also means less torque.
You're smart enough to know that, right?

Sigh.

They're related in a system.

I'll remain rigid on the mechanics. In 'Theory' the Ram 1500 is many times more capable than as advertised, but we have to de-rate it because people like this exist:

Sure. The 3.92 truck is just more capable.

View attachment 130209

Situational awareness is the best safety feature on your truck. But if you can't tow responsibly, I guess the 3.92 will solve all of your problems.

People who run into telephone poles exist?

 

[SnowBlaZR2]

Have you done the math?

What if the gear ratios in the tranny of an HD truck are taller than the 1500s? So that the actual final drive ratio of an HD with a 3.73 is the same as a half ton with a 3.21? Maybe an HD with 3.73 is already the same as a 1500 with 3.21.

A 1500 with 3.21 going down the highway at 80 MPH is turning about 1800 RPMs, I think (versus about 2200 RPMs with a 3.92). What RPMs is an HD with 3.73 turning at 80 MPH?

Just thinking about the gearing and tire size, I bet it would fall somewhere right in the middle.

Do you have the final ratios for the HD truck's transmission? Would be an interesting exercise, for sure.

 

[Ninety-9 SE-L]

Have you done the math?

What if the gear ratios in the tranny of an HD truck are taller than the 1500s? So that the actual final drive ratio of an HD with a 3.73 is the same as a half ton with a 3.21? Maybe an HD with 3.73 is already the same as a 1500 with 3.21.

A 1500 with 3.21 going down the highway at 80 MPH is turning about 1800 RPMs, I think (versus about 2200 RPMs with a 3.92). What RPMs is an HD with 3.73 turning at 80 MPH?

Do you happen to know the transmission ratios?

 

[SpeedyV]

Do you happen to know the transmission ratios?

Isn’t it exactly the same transmission (in the HD gasser)?

 

[Ninety-9 SE-L]

Isn’t it exactly the same transmission (in the HD gasser)?

Not sure.

The HD Diesel has the 3.73, the HD Gas has a 4.10. But I don't know what transmissions are shared with what other models.

 

[SnowBlaZR2]

Isn’t it exactly the same transmission (in the HD gasser)?

Assuming that is correct, and I didn't jack up the formulas, here's some math:



Someone check me on it, but looks like it'd fall pretty close to the middle, given the stock tire size (285/60R20) for a 2500 with a similar build.

 

[StuartV]

Assuming that is correct, and I didn't jack up the formulas, here's some math:

View attachment 130217

Someone check me on it, but looks like it'd fall pretty close to the middle, given the stock tire size (285/60R20) for a 2500 with a similar build.

Well, duh! If you ASSume they have the same transmission, then OF COURSE the RPMs for a 3.73 rear end are going to fall "somewhere in the middle" between a 3.21 and a 3.92...

LOL!!!

 

[SirHobgoblin]

Well, duh! If you ASSume they have the same transmission, then OF COURSE the RPMs for a 3.73 rear end are going to fall "somewhere in the middle" between a 3.21 and a 3.92...

LOL!!!

yes....but he actually did the math to produce quantifiable numbers that go beyond "somewhere in the middle".....

 

[SnowBlaZR2]

Well, duh! If you ASSume they have the same transmission, then OF COURSE the RPMs for a 3.73 rear end are going to fall "somewhere in the middle" between a 3.21 and a 3.92...

LOL!!!

You asked if I did the math. Well, there's the math.

They're just numbers.

 

[StuartV]

You asked if I did the math. Well, there's the math.

They're just numbers.

Well... I actually asked if you did the math with the HD tranny gear ratios. What I think you did is the math with the 1500 tranny gear ratios....?

 

[SnowBlaZR2]

Well... I actually asked if you did the math with the HD tranny gear ratios. What I think you did is the math with the 1500 tranny gear ratios....?

You asked "have you done the math?" Then asked some what ifs.

Do you have the ratios for the HD transmission, or any indication that it's not the same? Following the post above, the 8HP75-LCV in the 6.4 appears to be essentially the same as the 8HP75 in the 5.7, minus some upgraded internals.

 

[ferraiolo1]

He doesn’t do math. Because that’s factual vs hypothetical.


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[theblet]

What is this "math" thing everyone's talking about?

 

[SnowBlaZR2]

What is this "math" thing everyone's talking about?

I don't know, but if we can find it, I think we have a good chance of settling this topic.

 

[Dewey]

What is this "math" thing everyone's talking about?

I’ll do the math………

3.21’s @ 80 mph=1800 rpm’s
3.92’s @ 80 mph=2200 rpm’s

An extra 400 rpm’s is required to produce the same hp from the same motor. Extra rpm’s mean more fuel used.

If you like to drive fast and don’t tow much the choice is easy.

Enjoy

 

[djevox]

 

[SnowBlaZR2]

Extra rpm’s mean more fuel used.

Sounds like we need some more math...

 

[djevox]

Sounds like we need some more math...

I don’t know what hieroglyphics has to do with anything…