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 > 2021 Cummins 1075 lbft peak torque at 1356 rpm

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Grit dog

Black Diamond, WA

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Posted: 01/05/21 01:54pm Link  |  Quote  |  Print  |  Notify Moderator

4x4ord wrote:


7 th gear is 1:1 in the 10r140 and 6th is 1.277:1. So a downshift at 2114 rpm in 7th brings the engine speed to 2700 in 6th. 5th is 1.519 :1 so dropping from 6th at 2270 rpm would bring the engine up 2700 in 5th.


I hadn't looked at the ratios in a while. But looking at it, I'd drop 9th or 10th gear like a bad habit and stick with only 2 OD ratios and insert another gear somewhere between 4th and 7th, where the trans will spend most of it's time when loaded heavy.
400-500 rpm splits are great. About 100% better than my old 6 speed manual Dodge that was a challenge to get the next gear rolling before you lost 1000rpms.
But personal opinion, I'm not the guy who likes to see how low I can go on the tach and still get a load up a hill, because I've owned a couple EGT gauges and me and the EGT's are both much happier putting a few hundred more rpms through the input shaft. Thus, I don't need 3 OD ratios in a pickup truck, especially if it's not a 4.10 final ratio.
All good discussion! And pertinent to your torque rise examples. What if you could split that torq rise in half or even knock 30% off of it? Bingo, you're sitting at peak power availability more of the time. Whether you need all of it or not.
Which also helps with bsfc.


"Yes Sir, Oct 10 1888, Those poor school children froze to death in their tracks. They did not even find them until Spring. Especially hard hit were the ones who had to trek uphill to school both ways, with no shoes." -Bert A.

lenr

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Posted: 01/05/21 03:09pm Link  |  Quote  |  Print  |  Notify Moderator

So, this is the second thread that I have followed recently where the higher torque rise of the Cummins engine is discussed as a good thing. I have tried to think through why that is good, and all I can come up with is that it reduces the need to shift to a lower gear as load increases. In the days of manual transmissions shifting was something to be considered. With automatic transmissions, no big deal. As said above a downshift in a 3 or 4 speed transmission was a big jump in RMP, and again something to be minimized. Modern automatics are highly reliable and can shift without a reduction of longevity. The 8 to 10 speed transmissions exist to achieve the best ratio for given load and speed, so they need to shift to accomplish that. In my Ford with its less torque rise and a 6R140 transmission, gear hunting is not a problem, but if gear hunting starts, locking out a gear or switching to Tow-Haul mode solves it. Also, in a torque wars world where all the engines are similar at low end torque, I am fine with the engine having less torque rise since that means more HP at the top end. Top end HP is what accelerates my rig up to speed the fastest and pulls the mountain the fastest in whatever gear the transmissions determines. The Ford 6.7 consistently excels in HP while keeping up with the competition in torque.

RoyJ

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Posted: 01/05/21 03:41pm Link  |  Quote  |  Print  |  Notify Moderator

lenr wrote:

So, this is the second thread that I have followed recently where the higher torque rise of the Cummins engine is discussed as a good thing. I have tried to think through why that is good, and all I can come up with is that it reduces the need to shift to a lower gear as load increases. In the days of manual transmissions shifting was something to be considered. With automatic transmissions, no big deal. As said above a downshift in a 3 or 4 speed transmission was a big jump in RMP, and again something to be minimized. Modern automatics are highly reliable and can shift without a reduction of longevity. The 8 to 10 speed transmissions exist to achieve the best ratio for given load and speed, so they need to shift to accomplish that. In my Ford with its less torque rise and a 6R140 transmission, gear hunting is not a problem, but if gear hunting starts, locking out a gear or switching to Tow-Haul mode solves it. Also, in a torque wars world where all the engines are similar at low end torque, I am fine with the engine having less torque rise since that means more HP at the top end. Top end HP is what accelerates my rig up to speed the fastest and pulls the mountain the fastest in whatever gear the transmissions determines. The Ford 6.7 consistently excels in HP while keeping up with the competition in torque.


To see the benefit of torque rise, you'd have to look at the BSFC (brake specific fuel efficiency) curve / maps.

Hi torque rise is another way of saying near-constant hp within an rpm range. If you can "lug" an engine down to 2200 rpm and make the same hp as 2800 rpm, you often do so with better fuel efficiency. Here's a map (Shiner's) of the older engine:

[image]

This is why all big trucks (like that 2020 Volvo) are shifting towards low rpm / high torque, over revving it out like an old Detroit.

4x4ord

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Posted: 01/05/21 04:17pm Link  |  Quote  |  Print  |  Notify Moderator

If the goal is to win the race up the hill you're absolutely right, more gears and high horsepower get the job done. Consider the following scenario:

Think about what happens with the Powerstroke running up a hill heavily loaded, foot to the floor at ... 2500 rpm. Everything is wonderful. Now the grade increases from 6 to 6.5 % and the engine needs to deliver another 55 lb ft of torque (this would be the approximate value if you were towing a 20,000 lb trailer). The truck will slow down until that additional torque is delivered. (slowing down reduces the power required but the torque requirement does not change much at all). If you follow the torque curve of the Powerstroke you see that the slight increase in grade would bring the engine rpm down to 1600 rpm before it would be back at an equilibrium with the hill. So obviously it would slow down only to whatever rpm is necessary to bring about a shift. So, the truck would slow down and shift, then probably speed up a little and as soon as the hill levelled off just a bit it would accelerate shift up and slow down a bit again.

Now look at how the Cummins would handle the situation if it were running at 2500 rpm and the grade increased a bit requiring an additional 55 lbft of torque. The Cummins makes about 878 lbft of torque at 2500 rpm. With the high torque rise of the Cummins, torque builds rapidly and so by 2300 rpm it is making more than enough torque to satisfy the demands of the hill. When the hill levels off again the engine would speed back up to 2500 rpm.

* This post was edited 01/06/21 06:28am by 4x4ord *


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blofgren

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Posted: 01/05/21 09:19pm Link  |  Quote  |  Print  |  Notify Moderator

The low RPM massive torque while pulling with the Cummins is one of the things I noticed right away when I bought my truck over having 2 Ford PSD's. I need to hit a considerable hill while towing before having to downshift my truck out of 6th gear, and it is only on really tough pulls that I need to go down another gear from 5th.

The other thing I've noticed is that the Cummins never sounds like it's working hard, even when pulling heavy. I'm quite sold on the inline 6! [emoticon]


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FishOnOne

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Posted: 01/05/21 09:27pm Link  |  Quote  |  Print  |  Notify Moderator

blofgren wrote:

The low RPM massive torque while pulling with the Cummins is one of the things I noticed right away when I bought my truck over having 2 Ford PSD's. I need to hit a considerable hill while towing before having to downshift my truck out of 6th gear, and it is only on really tough pulls that I need to go down another gear from 5th.

The other thing I've noticed is that the Cummins never sounds like it's working hard, even when pulling heavy. I'm quite sold on the inline 6! [emoticon]


I noticed the same with my 6.7 PSD over my 6.0 PSD or even the lethargic 7.3. The 6.7 never feels like its stressed and pulling is a joy. I've been sold for +200k miles on the 6.7PSD.

Bottom line todays diesels are a huge improvement compared to the diesels not too long ago with the exception of emissions equipment. The guys who are running the 2020 6.7 PSD say it's a huge improvement over the early 6.7.


'12 Ford Super Duty FX4 ELD CC 6.7 PSD 400HP 800ft/lbs
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4x4ord

Alberta

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Posted: 01/05/21 10:15pm Link  |  Quote  |  Print  |  Notify Moderator

blofgren wrote:

The low RPM massive torque while pulling with the Cummins is one of the things I noticed right away when I bought my truck over having 2 Ford PSD's. I need to hit a considerable hill while towing before having to downshift my truck out of 6th gear, and it is only on really tough pulls that I need to go down another gear from 5th.

The other thing I've noticed is that the Cummins never sounds like it's working hard, even when pulling heavy. I'm quite sold on the inline 6! [emoticon]


If you like the way your 2013 Cummins pulls you'd be extremely impressed with the 2020 Powerstroke[image]

* This post was edited 01/05/21 10:33pm by 4x4ord *

Me Again

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Posted: 01/06/21 03:08am Link  |  Quote  |  Print  |  Notify Moderator

Do more gears always help. Last summer we bought a Ford Edge ST with the 2.7L twin turbo V-6 with 335hp and 380lbft. It was the new 8 speed transmission. The previous Edge Sport with 315HP and 6 speed transmission is slightly faster 0-60 and in the 1/4 mile.


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Grit dog

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Posted: 01/06/21 10:18am Link  |  Quote  |  Print  |  Notify Moderator

Me Again wrote:

Do more gears always help. Last summer we bought a Ford Edge ST with the 2.7L twin turbo V-6 with 335hp and 380lbft. It was the new 8 speed transmission. The previous Edge Sport with 315HP and 6 speed transmission is slightly faster 0-60 and in the 1/4 mile.


So you'd rather have the 6 speed to gain a tenth on 0-60 and trap speed and lose 2mpg?
It was a loaded question. But just like the throttle lag perception of some splitting hairs, 20hp gain and 1/10th sec slower may or may not be as a result of the transmission. Maybe 1 more shift caused a 3/10th drop and the extra 20 ponies made 2/3 of it back. (The fastest transmissions still take about 200 milliseconds to shift) The high winding motor probably doesn't need the extra cogs for performance, but rather economy. Maybe the new one has 100lbs more "options" or a different traction control program that pulled back a smidge of power off the line to keep from squeaking the tires with a lower first gear and extra 20hp.
Maybe the turbo is tuned slightly different....
Any number of factors tht neither you nor I are smart enough to figure out, to blame it on the trans.

My question would be, why did you get the new one if you really wanted 2 less gears and .1 seconds faster?
Or in other words, not pertinent to the discussion at hand, but they are cool little fast cars!

4x4ord

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Posted: 01/06/21 10:56am Link  |  Quote  |  Print  |  Notify Moderator

Grit dog wrote:

4x4ord wrote:


7 th gear is 1:1 in the 10r140 and 6th is 1.277:1. So a downshift at 2114 rpm in 7th brings the engine speed to 2700 in 6th. 5th is 1.519 :1 so dropping from 6th at 2270 rpm would bring the engine up 2700 in 5th.


I hadn't looked at the ratios in a while. But looking at it, I'd drop 9th or 10th gear like a bad habit and stick with only 2 OD ratios and insert another gear somewhere between 4th and 7th, where the trans will spend most of it's time when loaded heavy.
400-500 rpm splits are great. About 100% better than my old 6 speed manual Dodge that was a challenge to get the next gear rolling before you lost 1000rpms.
But personal opinion, I'm not the guy who likes to see how low I can go on the tach and still get a load up a hill, because I've owned a couple EGT gauges and me and the EGT's are both much happier putting a few hundred more rpms through the input shaft. Thus, I don't need 3 OD ratios in a pickup truck, especially if it's not a 4.10 final ratio.
All good discussion! And pertinent to your torque rise examples. What if you could split that torq rise in half or even knock 30% off of it? Bingo, you're sitting at peak power availability more of the time. Whether you need all of it or not.
Which also helps with bsfc.



[image]
I agree with not needing 3 OD gears. Even if 10th is left at .632:1 we don't need two gears to get there. Pulling hard in OD is not really what we want for reasons like you mention as well as there is a loss in power speeding the drive shaft up just to slow thigs down again at the rear axle. Even so 63 mph is 2000 rpm with 3.55 final drive and 8th gear. The Powerstroke is putting out 400 HP at 2000 rpm so 8th gear is definitely a gear that can be used for pulling hard and it is a high enough ratio to use for light loads that 10th can't handle... we don't need 9th.

Maybe more gears between 4th and 7th would be good. The problem with more gears in between 4th and 7th is determining how to use them. With a manual transmission I can select the ratio I want depending on all sorts of parameters that I have in mind ... things like preparing for the up coming hill or slowing down for the stop sign ahead or keeping the engine brake quiet or whatever else I have in mind. An automatic can't read my mind and so it might shift up right about the time I floor the accelerator to pass someone and now it has to drop three gears. Or it might down shift right about the top of the hill and we could probably come up with all sorts of circumstances that would trigger annoying shifts especially if the ratios get too close together.

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