2025 Ram trucks

[dieselscout80]

Correct it’s not a rule but rather an example.

 

[WinterDeere]

It all depends….
Depending on what other aspects of the design are kept constant.
You could conversely claim, a larger bore tends to produce more torque than a smaller bore, assuming the stroke is kept the same.

True. But it's also true that the inline 6's tend to be built with the longer stroke/bore ratio, and that for the same CID, longer stroke favors higher torque. What you're discussing, keeping the same stroke and increasing bore, is increasing displacement.

There’s no technical reason a V8 can’t have as long a stroke as a straight 6, or that a straight 6 can’t have as large a bore as a v8.

Seeing as how the convention has developed to put the longer stroke/bore ratio in the inline 6's, versus the v8's, I actually suspect there is some technical reason for it. Engineers don't operate on whims, there must be good reasons for these trends being so prevalent. As to whether those reasons are "technical", might just depend on how broadly you define that word.

 

[ericm979]

I think with modern turbo engines, tuning has a greater effect on low rpm power (what most people mean by "torque") than bore and stroke.

I was curious so I dug up the bore/stroke numbers for the three HD pickup engines, and their power curves:

Bore x Stroke:

Cummins 6.7: 107x124

Powerstroke: 99x108

Duramax: 103x99

The mildly undersquare Ford wins both for peak hp and torque and low rpm hp and torque, the more undersquare Cummins comes in last, with the mildly oversquare GM in the middle. The Cummins signs off the soonest though at an rpm that's well past the power peak for any of the engines.

 

[Hay Dude]

The other great thing about in-line six configurations is they are cheaper to build/buy & maintain.
They get better fuel economy
Their crankshaft is stronger because its supported by more bearings

Thats why in line sixes are most prevalent in heavy tractors and OTR trucks.

 

[Hay Dude]

I think with modern turbo engines, tuning has a greater effect on low rpm power (what most people mean by "torque") than bore and stroke.

I was curious so I dug up the bore/stroke numbers for the three HD pickup engines, and their power curves:

Bore x Stroke:

Cummins 6.7: 107x124

Powerstroke: 99x108

Duramax: 103x99

The mildly undersquare Ford wins both for peak hp and torque and low rpm hp and torque, the more undersquare Cummins comes in last, with the mildly oversquare GM in the middle. The Cummins signs off the soonest though at an rpm that's well past the power peak for any of the engines.

Interesting/suspicious on your charts they didn’t use the high output (HO) Cummins in the comparison.
It made 400HP and 1075 TQ.
Must be a chart bought & paid for by GM & Ford….lol

 

[ericm979]

Interesting/suspicious on your charts they didn’t use the high output (HO) Cummins in the comparison.

They also did not include the high output Ford. Or the '23 on higher output Duramax.

I'm not trying to put down any brand, just posting data about the actual low rpm power of the different engine configurations and bore/stoke ratios. Clearly all the engines make more than enough power for their intended use.

 

[Hay Dude]

They also did not include the high output Ford. Or the '23 on higher output Duramax.

I'm not trying to put down any brand, just posting data about the actual low rpm power of the different engine configurations and bore/stoke ratios. Clearly all the engines make more than enough power for their intended use.

‘23 Dmax is 2 years newer than the other 2. Best way to compare things is compare same years.
I’d compare all 2021’s, all 2022’s, etc.

Also interesting to point out although having the lowest HP rating, the Ram had the highest towing capacity on most models.
In 2020, the Ram I bought had a GCWR of 43,000. Comparable F-550 and GM-5500 were lower with a GCWR of only 40,000

 

[Renze]

True. But it's also true that the inline 6's tend to be built with the longer stroke/bore ratio, and that for the same CID, longer stroke favors higher torque. What you're discussing, keeping the same stroke and increasing bore, is increasing displacement.

Most important reason that the common idea is that long stroke means more low end torque, is because in naturally aspirated, 2 valves per cylinder engines, the valve diameter limits high rpm breathing on an undersquare engine vs an equal capacity oversquare engine, just because you can put larger diameter valves in a head atop a larger bore engine. There might be other factors involved, but i am a well informed tech enthusiast, not an engine guru.

Either way, i think the mediocre V8 diesels at Cummins and Cat, contributed to the popularity of the Cummins inline 6 in the Ram...

Seeing as how the convention has developed to put the longer stroke/bore ratio in the inline 6's, versus the v8's, I actually suspect there is some technical reason for it. Engineers don't operate on whims, there must be good reasons for these trends being so prevalent. As to whether those reasons are "technical", might just depend on how broadly you define that word.

To get the displacement from less cylinders, you need larger pistons making it an undersquare engine, or if you dont want that, you need to upsize both bore and stroke.

The latter causes a higher piston speed at a given RPM, resulting in more wear.

If you look at the 1960s V8 diesels, they generally had a higher rpm so despite the short stroke, piston speed of a V903 was comparable to an NT855 (or whatever predecessor had 330hp turbo power at 2000rpm in the early 60s)while the V903 had the same power at 2800rpm.

The same thing still counts for pickup truck diesels: You can either add two cylinders with a shorter absolute stroke, so you can elevate its redline to gain horsepower, or you can choose an inline 6 configuration with a lower redline and less complex but beefier internals to make the hp at a slightly lower rpm.

Industrial versions of the B6.7 top out at 300hp or so, much lower than the medium duty versions used in pickups with a higher horsepower rating.

The FPT NEF67 puts out 340 engine hp in the Case Puma 340, i cant think of any tractor engine with 45hp per liter. They can do so because they dont use EGR, so the turbo can pump clean air into the engine and doesnt have to work to put 20 to 30% EGR back into the cylinders...

 

[Snobdds]

The other great thing about in-line six configurations is they are cheaper to build/buy & maintain.
They get better fuel economy
Their crankshaft is stronger because its supported by more bearings

Thats why in line sixes are most prevalent in heavy tractors and OTR trucks.

You have one mode...

 

[Snobdds]

You seem to be hung up on the turbo. Turbo chargers need RPM to produce airflow which in turn produces power. So no, the turbo has nothing to do with the fact that a diesel engine makes amazing torque just off idle. "Off idle" means what it says...just off idle, i.e. just above the point where the engine is idling. At those RPMs the turbo is doing very little.

I'm hung up because it's what makes the low end torque.

For example, on the 6.0 powerstroke, the motor that taught me. The 2003-2004 had a 10 blade compressor blade on the turbo. The 2005-2007 had a 13 blade compressor blade on the turbo. It was noticeable how much more low end torque there was on the 03-04 vs the 05-07. The flip side to that same coin was the 03-04 ran out of air once you hit 65. The 05-07 had slightly less air at the low RPM, but the air was still coming on at 65-75. I have yet to see a variable compressor wheel to a turbo. There are variable turbine side vanes that help with spooling a turbo when starting out.

Once you realized the physics at play, your understand what brings on the torque...air being forced into an engine to produce power.