2021 HD diesel pull tests...

[432bartman]

Originally Posted by firestation12

A few qualifiers to mention here. The Ram truck was competing with a 6 speed transmission. The Ford and Chevy had 10 speed close ratio transmissions. The Chevy had the lowest axle ratio of 3.73 (standard on the 6.6 Duramax 2500) which is an advantage over the Ford’s either available 3.31 or 3.55 (the article doesn’t specify which axle was in the test truck), and lastly, the Ford was torque limited until reaching 4th gear and the Chevy was not. I find it hard to come to a conclusion of a winner. The Ram did very well considering the 2500 has a de-rated 370 hp. Only the 3500 Ram truck is available With the high output Cummins and Aisin transmission (still a 6 speed).

The 2020 and up Chevy/GM's only come with a 3:43 rear-end, and that is both for the 2500 & 3500's. The gas motor comes with a 3:73.

[kowbra]

Originally Posted by 432bartman

The 2020 and up Chevy/GM's only come with a 3:43 rear-end, and that is both for the 2500 & 3500's. The gas motor comes with a 3:73.

Interesting; maybe due to the 10 speed transmission change?
RAM cummins went the other way; in 2019+ they switched to a 3.73 rear axle ratio where years prior were 3.42.

The 3.73 with the 6 speed transmissions make a lot more sense for the RAM cummins. The peak torque (usually the most efficient rpm for a diesel) is at 1800rpm. With the 3.42s, 1800rpm puts you at about 65mph, whereas the prior generation was at 72mph.

So, especially when towing heavy, 6th gear at 65mph puts you right in the peak power band; exactly as it should be.

BTW, if you want to check out a cool tool to calculate this, see here

Now, if RAM puts the rumored ZF 8 speed in the cummins models? That could likely shake things up again.

Brad

[mlh]

The peak torque (usually the most efficient rpm for a diesel) is at 1800rpm

Peak torque is always the most efficient RPM for any ICE engine. You get the most work done for the amount of fuel used. That is not to say you get the best fuel mileage. Let’s say you have a really high geared truck and would be moving at a hundred MPH at peak torque in this case 1800 RPM. Wind resistance and friction would cause you to use more fuel than you would use at a lower speed.
Lynwood

[DadsHemi]

Originally Posted by kowbra

Interesting; maybe due to the 10 speed transmission change?
RAM cummins went the other way; in 2019+ they switched to a 3.73 rear axle ratio where years prior were 3.42.

The 3.73 with the 6 speed transmissions make a lot more sense for the RAM cummins. The peak torque (usually the most efficient rpm for a diesel) is at 1800rpm. With the 3.42s, 1800rpm puts you at about 65mph, whereas the prior generation was at 72mph.

So, especially when towing heavy, 6th gear at 65mph puts you right in the peak power band; exactly as it should be.

BTW, if you want to check out a cool tool to calculate this, see here

Now, if RAM puts the rumored ZF 8 speed in the cummins models? That could likely shake things up again.

Brad

Peak tq on an ISB 6.7 is 1700 rpm and peak HP 2800 rpm
With 4:10s at 65 I turn 1730 rpms on my Dually.

[kowbra]

Originally Posted by DadsHemi

Peak tq on an ISB 6.7 is 1700 rpm and peak HP 2800 rpm
With 4:10s at 65 I turn 1730 rpms on my Dually.

Sounds about right for speed and rpms. Of course, will vary with tire size also.

For 2019+, Cummins totally rebuilt the 6.7 using a different block and saving over 60lbs. They also were the first pickup to get to 1000lbs of torque (with the HO option), but now torque peaks at 1800 rpm. (when the 6.7 first went into RAMs, I think the peak torque was at 1600rpm)

With the 3.42s on both my 2014 and 2016, it was about 1600rpm at 65, and the truck just felt stronger at about 70mph/1700rpm.

I will say the driving experience is noticeably different with the 3.73s. The pedal response is much improved, especially off the line. I don't think the 3.42s with a 6 speed was ever ideal; the truck was often at 1000-1100rpm around town, empty and without tow/haul mode. Of course the cummins did the job, but with the 3.73s and an extra 100-200rpm, it just feels like it's breathing better. (they've retuned the shift points also though)

Now, of course with the 4.10s you have a different experience again, and a much stronger pull. And, I see you have a tune, so you've probably got a towing beast there!

Brad

[432bartman]

Originally Posted by kowbra

Interesting; maybe due to the 10 speed transmission change?
RAM cummins went the other way; in 2019+ they switched to a 3.73 rear axle ratio where years prior were 3.42.

The 3.73 with the 6 speed transmissions make a lot more sense for the RAM cummins. The peak torque (usually the most efficient rpm for a diesel) is at 1800rpm. With the 3.42s, 1800rpm puts you at about 65mph, whereas the prior generation was at 72mph.

So, especially when towing heavy, 6th gear at 65mph puts you right in the peak power band; exactly as it should be.

BTW, if you want to check out a cool tool to calculate this, see here

Now, if RAM puts the rumored ZF 8 speed in the cummins models? That could likely shake things up again.

Brad

The new 10 speed was geared lower than the 6 speed it replaced, which allowed for even better pulling power with the 3:42 rearend.

[Bad Moon]

Originally Posted by scottz

You are thinking of the Davis Dam grade, in Arizona between the Colorado river (Laughlin, NV) and Kingman on Hwy 68. Was on it a few weeks ago; no problem.
https://fifthwheelst.com/SAE-J2807-Tow-Tests.html

There is a video from 2019 or 2020 that shows the Ford SD factory test vehicle on the Davis Dam Grade, parked on the shoulder. On fire. :-)