Why do you Cummins guys want more gears

4x4ord wrote:

Grit dog wrote:

4x4ord wrote:

Groover wrote:
Whenever the transmission upshifts to 4th or 5th gears I lose nearly a third of my RPM and a lot of my acceleration or hill climbing. I would dearly love to have another gear in that range as well as a lower first gear so things would get moving a little more quickly while waiting for the turbo to wind up.

So yeah, I would love to have 8 to 10 gears to choose from.

What you are experiencing is the lack of torque rise in your current engine.

No, Groover is right. He's experiencing lack of gears.

Lack of gears vs lack of torque rise... the consequence at the rear wheels is identical.

To quote you earlier in this thread..." I could see an 8 speed possibly being a slight improvement over the current Aisin 6 speed but I would rather have 6 gears behind the Cummins than 10. The Powerstroke doesn't have the same torque rise that the Cummins has so in order for it to make use of its 475 HP it needs more gears."

So you're (correctly) stating that the Cummins has more torque rise than the Pstroke (and the Dmax).
How much more torque rise can you get out of a light duty truck diesel?
Cummins design is about as good as it gets for torque rise, hence why it can get by with less gears all other things equal.

4x4ord wrote:

Grit dog wrote:
And the ZF 8HP isn't going behind the Cummins.

Do you know of any transmission options available to Ram that would work well behind the Cummins?

Yes... The mighty Allison. ATS Diesel Performance has a Allison conversion kit to put a Allison behind the Cummins. They also refer to the 68RFE as a half ton gas transmission that has design roots to the Chrysler Caravan. ATS doesn't speak to highly of the Aisin either as they're extremely expensive to repair.

Link

Grit dog wrote:
And the ZF 8HP isn't going behind the Cummins.

Do you know of any transmission options available to Ram that would work well behind the Cummins?

Grit dog wrote:

4x4ord wrote:

Groover wrote:
Whenever the transmission upshifts to 4th or 5th gears I lose nearly a third of my RPM and a lot of my acceleration or hill climbing. I would dearly love to have another gear in that range as well as a lower first gear so things would get moving a little more quickly while waiting for the turbo to wind up.

So yeah, I would love to have 8 to 10 gears to choose from.

What you are experiencing is the lack of torque rise in your current engine.

No, Groover is right. He's experiencing lack of gears.

Lack of gears vs lack of torque rise... the consequence at the rear wheels is identical.

schlep1967 wrote:
I don't care how many gears it has. I just want it to allow me to pull the trailer up hills and not break when I need it.
If they need to make the gears a lighter weight more suseptable to breakage to get them all in he transmission, I'd prefer fewer heavier gears and reliability.

I feel as you do but the important thing to me is have a truck that matches what it needs to tow. 5 gears works great for us. chevman

"Lugging is certainly not good for the engine. You need more gears to keep the engine in the ideal RPM range over varying conditions."

My CUMMINS/AISIN combo simply will NOT under any circumstances "LUG" the engine. Tow Haul on and it's always in it's power band.

ShinerBock wrote:

4x4ord wrote:


I’ve heard people refer to automatics as slush boxes before but I’ve never really thought about it. You’re saying the ZF 8HP is not a slush box. By that I’m guessing “slush box” doesn’t simply mean automatic but a slow shifting automatic? Is the ZF you’re referring to a double clutch or what makes it special? Is it a candidate for the Ram trucks?

Slush box transmissions are generally clunky and slow shifting similar to those found in commercial trucks. While the Aisin is stout, it is clunky and very slow to shift so you are going to win any 0-60 battles in that thing. The 68RFE is quicker, but it is still a slush bosh in my opinion.

The ZF 8HP speed found in many BMW's, Ram's(1500 and 2500 gassers), Jeeps, and many other vehicles is a whole different animal. Shifts are smooth, quick, and precise. With my car in sport mode, you can't even feel the shift happen it is so quick. It is not a double-clutch, but it is just as quick as one without the very harsh shifts.

It is even quicker than the previous ZF 6HP which is what the 6R80 in my old F150 and the 6R140 in the SD's were based on. While Ford did build the 6R line of transmission in-house, they had ZF design it based on the 6HP and they used that same design in the 10R line, but with more clutches/gears. In my opinion, the ZF 8-speed is quicker/smoother than the Ford 10-speed after driving my car and my nephew's Ecoboost Mustang back to back.

Engineering Explained can probably explain it better than me.

The World's Best Automatic Transmission

Very impressive transmission. Thanks for posting the link.

And the ZF 8HP isn't going behind the Cummins.

Groover wrote:

mkirsch wrote:

SweetLou wrote:
Not needed. More speed towing is dangerous for many reasons, and you achieve a good speed now. Lugging any engine while pulling a weight not good either. Continual searching for correct gears can't be good. The best overall range for towing with that Cummins is around 1800 RPM so in my opinion not needed.

Most of what you said is an argument FOR more gears.

Lugging is certainly not good for the engine. You need more gears to keep the engine in the ideal RPM range over varying conditions.

This raises the question of what is the definition of lugging and engine? Every vehicle that I own keeps the engine turning as slow as it can while providing the required power, presumably for fuel economy. I frequently force a downshift but I also wonder what the thought process was for the engineers that are designing those drivetrains and what they consider lugging to be.

Lugging is when you are in too high of gear at a low rpm(generally below peak torque) with your foot past 75% throttle and the truck is not accelerating or barely accelerating. You will generally see your EGT's spike when lugging. This cannot be done in an automatic because it would shift way before it gets to this point. It can only be done in a manual trans unless the auto trans is specifically tuned to do so.

I have a tune that will allow my engine all the way down to 950 rpm and even then it is not lugging since it has enough torque that low to easily accelerate under light throttle when unloaded even up slight hills. Of course, I get my best fuel mileage on this tune since it keeps the RPMs low when not towing, however, it is not an ideal tune for towing.

4x4ord wrote:


I’ve heard people refer to automatics as slush boxes before but I’ve never really thought about it. You’re saying the ZF 8HP is not a slush box. By that I’m guessing “slush box” doesn’t simply mean automatic but a slow shifting automatic? Is the ZF you’re referring to a double clutch or what makes it special? Is it a candidate for the Ram trucks?

Slush box transmissions are generally clunky and slow shifting similar to those found in commercial trucks. While the Aisin is stout, it is clunky and very slow to shift so you are going to win any 0-60 battles in that thing. The 68RFE is quicker, but it is still a slush bosh in my opinion.

The ZF 8HP speed found in many BMW's, Ram's(1500 and 2500 gassers), Jeeps, and many other vehicles is a whole different animal. Shifts are smooth, quick, and precise. With my car in sport mode, you can't even feel the shift happen it is so quick. It is not a double-clutch, but it is just as quick as one without the very harsh shifts.

It is even quicker than the previous ZF 6HP which is what the 6R80 in my old F150 and the 6R140 in the SD's were based on. While Ford did build the 6R line of transmission in-house, they had ZF design it based on the 6HP and they used that same design in the 10R line, but with more clutches/gears. In my opinion, the ZF 8-speed is quicker/smoother than the Ford 10-speed after driving my car and my nephew's Ecoboost Mustang back to back.

Engineering Explained can probably explain it better than me.

The World's Best Automatic Transmission