6.7 Cummins vs 6.6 Duramax

[SoonerWing03]

As someone who knows next to nothing about Diesel engines, I am trying to figure out the strengths and weaknesses of these to. Any opinions would be appreciated.

[IdaD]

I feel like my 2015 Cummins acts like it's a little more relaxed when towing compared to my brother in law's 2015 or 2017/8 Powerstroke. The Ford feels quicker empty, but it seems like the trailer taxes it a little harder towing. They're both extremely good tow vehicles, obviously. I haven't towed in a recent model Duramax so I can't compare it. I think we've all seen enough objective testing to know that the three of them are all plenty good from a towing performance standpoint, and then personal preference will come into play.

I will say that up to recently I would definitely take the Cummins over either the Duramax or Powerstroke. If you're talking 2019+ models, I think I'd opt for the Duramax since the Cummins went to the CP4 pump.

[ShinerBock]

Most trains and certain ships use V configurations to fit in tight spaces versus a longer I configuration. Most big ships where a compact space is not an issue and efficiency is more important, an inline engine is used.

[campigloo]

The physics lesson has been fun.
Out of the three of them, I still like my Ram the best. I say get the pretty one. The thing I’m not too crazy about is the dark blue exterior and dark gray interior. They initially look great but are hard to keep clean. We always try avoid any sentence or thought that includes the word dirt. We do like the
4x4 feature except for the fact that I have to have a ladder to wash it (but the ladder allows a longer stroke while I’m still the same displacement).
Happy shopping, I’m jealous!

[SoonerWing03]

Grit dog wrote:
I'm guessing Soonerwing03 couldn't give 2 schitts about all this....
Maybe we could get back to complaining about why he has a lift kit on his current rig, then he could participate in the fun!

LMAO

Probably because I am compensating for having a small sinep. Lol

Bought the Tahoe in June of 17. Went camping to CO over Labor Day weekend 17’ and Memorial Day weekend 18’ sleeping in a tent. Wife said no more freezing her butt off so we bought the TT in July 18’. Economics of trading in the Tahoe weren’t too appealing at the time and still aren’t which is why I am considering hanging onto it and passing it down through the 3 boys as each of their first car. Downside to that is that their second vehicle is going to suck compared to their first I guess. Well maybe not the baby, it may be in rough shape 6.5 years from now and two 16 year old's later.

[RCMAN46]

Pulls like a train.

You all do realize most modern trains have V16 diesel engines. As are many of the current cruise ship diesel engines are V models.

Boy step on the Cummins by stating long stroke engines have higher piston speeds and all h$ll breaks loose.

[Grit_dog]

I'm guessing Soonerwing03 couldn't give 2 schitts about all this....
Maybe we could get back to complaining about why he has a lift kit on his current rig, then he could participate in the fun!

[ShinerBock]

ShinerBock wrote:

4x4ord wrote:

This bit about natuaral torque coming from a longer stroke is bs. If the displacement remains the same that longer stroke is going to dictate a smaller bore. Torque is a reflection of the amount of heat energy released from the fuel during a power stroke. So it is a function of cylinder volume and volumetric efficiency.



Edit: besides the above the Powerstroke has a longer stroke than the Cummins...... does this mean the Powerstroke pulls like a freight train compared to a Cummins.:)

Torque = force x distance. Longer stroke = longer distance. If two engines are generating the same force to the top of that piston, but one has longer rod turning the crank, then it will have more torque.

Also, the 4.88 inch stroke of the Cummins is much longer than the 4.25 inches of the Powerstroke, and both are longer than the 4.06 inches of the Duramax.

Correction, the Duramax has a 3.89 inch stroke, not a 4.06 inch stroke.

[4x4ord]

ShinerBock wrote:

4x4ord wrote:

This bit about natuaral torque coming from a longer stroke is bs. If the displacement remains the same that longer stroke is going to dictate a smaller bore. Torque is a reflection of the amount of heat energy released from the fuel during a power stroke. So it is a function of cylinder volume and volumetric efficiency.



Edit: besides the above the Powerstroke has a longer stroke than the Cummins...... does this mean the Powerstroke pulls like a freight train compared to a Cummins.:)

Torque = force x distance. Longer stroke = longer distance. If two engines are generating the same force to the top of that piston, but one has longer rod turning the crank, then it will have more torque.

Also, the 4.88 inch stroke of the Cummins is much longer than the 4.25 inches of the Powerstroke, and both are longer than the 4.06 inches of the Duramax.

You're right the Cummins has a longer stroke than the Powerstroke ... that was my bad. But stroke length makes no difference to torque if you keep the same displacement. Think of the pressure on the top of the piston in psi. A smaller piston with a longer stroke and or less pistons with a longer stroke means less force on that longer lever. If you think about it you'll come to realize that overall displacement and volumetric efficiency determine the amount of fuel that can be utilized per revolution which determines the torque output of an engine.

[ShinerBock]

wnjj wrote:
Well in 2017 at least it would appear that the Duramax managed to out-freight train the Cummins:
https://images.app.goo.gl/FdYZ41ETQaEqeZLQ9

When an engine achieves peak on a wheel end dyno is not accurate. A lot of things come into play like how the torque converter locks up and at what gear. Then there is torque management which makes it even harder to depending on the vehicle. Trying to get it just right on certain dynos is down right tricky from one vehicles tot he next.

Wheel end dynos are also done at wide open throttle and the "pull like a train" people are referring to is at low rpm part throttle(normal driving) when the turbo does not come into play as much.

[wnjj]

Well in 2017 at least it would appear that the Duramax managed to out-freight train the Cummins:
https://images.app.goo.gl/FdYZ41ETQaEqeZLQ9

[ShinerBock]

4x4ord wrote:

This bit about natuaral torque coming from a longer stroke is bs. If the displacement remains the same that longer stroke is going to dictate a smaller bore. Torque is a reflection of the amount of heat energy released from the fuel during a power stroke. So it is a function of cylinder volume and volumetric efficiency.



Edit: besides the above the Powerstroke has a longer stroke than the Cummins...... does this mean the Powerstroke pulls like a freight train compared to a Cummins.:)

Torque = force x distance. Longer stroke = longer distance. If two engines are generating the same force to the top of that piston, but one has longer rod turning the crank, then it will have more torque.

Also, the 4.88 inch stroke of the Cummins is much longer than the 4.25 inches of the Powerstroke, and both are longer than the 4.06 inches of the Duramax.

[4x4ord]

ShinerBock wrote:

RCMAN46 wrote:
"They also operate at lower engine rpms, which lowers the piston speed. Pretty much an irrelevant negative on the I-6!"

If you are comparing the Cummins with the Duramax then you are dead wrong.


Here are the facts.

The Cummins makes its peak torque at 1800 rpm
The Duramax makes its peak torque at 1600 rpm

The Cummins makes its max horsepower at 2800 rpm.
The Duramax makes its max horsepower at 2800 rpm.

So much for the popular belief that the I6 Cummins operates at a lower rpm than the v8 Duramax.

So the statement that the Cummins operates at a higher piston speed holds true when comparing to the Duramax.

While I have been trying to stay away from this pissing match thread, there is more to this than peak torque/horsepower at wide open throttle where hardly any one drives at. The RPM peak torque is achieved at wide open throttle is mainly dictated by electronically controlled VG turbos anyways. However, under normal driving conditions there is what I refer to as natural torque and boost assisted torque and makes a bug difference in how the truck drives when not at wide open throttle.

Due to the longer stroke of the Cummins, it makes more natural low end torque without the assistance of the turbo. This is why people always say a Cummins pulls like a train because it generates so much torque at low revs under normal driving conditions. This is also why Pickuptrucks.com and a few of the other review sites have said that the Cummins feels least phased by loads compared to the other two under normal driving conditions especially under 1,600 rpm.

The short stroke Duramax on the other hand utilizes the turbo more to achieve its torque at low rpm under normal driving conditions. Giver here the throttle and it will blow the doors off of the Ram, but it feels likes it has less torque under 1,600 rpm versus the Cummins in normal driving conditions until the turbos are spooled. When I was driving my cousins L5P, you did not get the same torque pull feel until higher rpms as you did on my truck at just 1,400 rpm.

Not trying to dis the Duramax because it is a great engine and is very quick at wide open throttle in stock form versus the other two if that is what you are after, but it does feel like it has less torque at low rpms in normal driving conditions versus the Cummins regardless of when it's turbo is programmed to achieve peak torque at wide open throttle. Drive and tow with both back to back and you will see what mean. My brother even says the same about his old 2012 PSD versus his current 2014 CTD and my father in law with his 2018 PSD versus my CTD.

This bit about natuaral torque coming from a longer stroke is bs. If the displacement remains the same that longer stroke is going to dictate a smaller bore. Torque is a reflection of the amount of heat energy released from the fuel during a power stroke. So it is a function of cylinder volume and volumetric efficiency.



Edit: besides the above the Powerstroke has a longer stroke than the Cummins...... does this mean the Powerstroke pulls like a freight train compared to a Cummins.:)

[memtb]

Me Again wrote:

memtb wrote:


If it floats, flies, or rolls....it was meant to be raced!

And you speed shift your RAM manual tranny, NOT!

I never said that I “race” my truck.....only defended those that want to to do so! It’s really “not” that complicated! For most people!:S

[ShinerBock]

RCMAN46 wrote:
"They also operate at lower engine rpms, which lowers the piston speed. Pretty much an irrelevant negative on the I-6!"

If you are comparing the Cummins with the Duramax then you are dead wrong.


Here are the facts.

The Cummins makes its peak torque at 1800 rpm
The Duramax makes its peak torque at 1600 rpm

The Cummins makes its max horsepower at 2800 rpm.
The Duramax makes its max horsepower at 2800 rpm.

So much for the popular belief that the I6 Cummins operates at a lower rpm than the v8 Duramax.

So the statement that the Cummins operates at a higher piston speed holds true when comparing to the Duramax.

While I have been trying to stay away from this thread, there is more to this than peak torque/horsepower at wide open throttle where hardly any one drives at. The RPM peak torque is achieved at wide open throttle is mainly dictated by electronically controlled VG turbos anyways. However, under normal driving conditions there is what I refer to as natural torque and boost assisted torque and makes a bug difference in how the truck drives when not at wide open throttle.

Due to the longer stroke of the Cummins, it makes more natural low end torque without the assistance of the turbo. This is why people always say a Cummins pulls like a train because it generates so much torque at low revs under normal driving conditions. This is also why Pickuptrucks.com and a few of the other review sites have said that the Cummins feels least phased by loads compared to the other two under normal driving conditions especially under 1,600 rpm.

The short stroke Duramax on the other hand utilizes the turbo more to achieve its torque at low rpm under normal driving conditions. Giver here the throttle and it will blow the doors off of the Ram, but it feels likes it has less torque under 1,600 rpm versus the Cummins in normal driving conditions until the turbos are spooled. When I was driving my cousins L5P, you did not get the same torque pull feel until higher rpms as you did on my truck at just 1,400 rpm.

Not trying to dis the Duramax because it is a great engine and is very quick at wide open throttle in stock form versus the other two if that is what you are after, but it does feel like it has less torque at low rpms in normal driving conditions versus the Cummins regardless of when it's turbo is programmed to achieve peak torque at wide open throttle. Drive and tow with both back to back and you will see what mean. My brother even says the same about his old 2012 PSD versus his current 2014 CTD and my father in law with his 2018 PSD versus my CTD.

[Me_Again]

memtb wrote:


If it floats, flies, or rolls....it was meant to be raced!

And you speed shift your RAM manual tranny, NOT!