Gentlemen. Read post #545 on this thread. I went through the math. A PSD will tow more weight, and up to higher speeds, too.

It seems from the follow-up posts that most of you did not "get it". For example Dispenser was all worried about have the EXACT torque numbers. The torque numbers I used were ballpark. I.e. 585 or 590 ... doesn't make any difference. The Torque x RPM at any given point is the amount of work the engine can do. As weight is added to the trailers ... both engines needed to downshift alternatingly. The dodge runs out of oomph, and the PSD can keep speed with the higher tow-load.

The sorter version is this:
600 ft-lbs x 1600 is LESS than 560 ft-lbs x 2000 RPM

Dispencer keeps showing his 5th grade ejukation level by muttering his mantra "325 and 600 is better than 325 and 560". Well ... sherlock .... I got news for ya. It ain't my friend. I can't think of any way to show show your complete ignorance of engine-physics than to completely ignore engine RPM.

This has NOTHING to do with gearing, either. Ford is not make something with "LESS FORCE" as Lunatic put it to suddenly do more.

SUMMARY .... REPEAT .... SUMMARY:
The WORK produced by an engine is TORQUE (a force, but in ft-lbs) times RPM's (in radians, which is unitless). The RESULT is WORK (in ft-lbs ... a different ft-lbs than what the torque is.

CUMMINS: 600 ft-lbs x 1600 rpm (1rev/ 2-pi radians) = 152,866 ft-lbs

PSD: 560 ft-lbs x 2000 rpm (1 rev/ 2-pi radians) = 178,343 ft-lbs

Again, if you are completely ignorant, with little to no education, and closed-minded to teaching and instruction, with just barely the intelligence to read a Dodge brochure, this is what you say (which is meaningless):

Cummins has 325 hp and 600 ft-lbs of torque
PSD has 325 hp and 560 ft-lbs of torque

You follow this up with the wildly inane bold-faced lie that therefore the Cummins is "better" and can do "more work".

(I'm hoping some repetitive explanation will sink in ... let's cross our fingers).

MARINE IRONMAN

 

I'm hoping some repetitive explanation will sink in

Not a chance..........your post is #556...how many could it take

 

I may be ignorant and not real smart HOWEVER try doing your figuring comparing same rpms, not different. 2000 and 1600 are different. 2000 and 2000 are same. 1600 and 1600 are same. At both these rpms (and at all points from idle) when you compare rpms you find the cummins is higher than psd. At All Points.

One of these days maybe you will compare fairly. I haven't seen it yet. I challenge you to do your figures rpm vs rpm. AT ANY POINT UNDER 2900rpm. Then you will see what your figures still point out.......when using LIKE comparisons........
The 1600 cummins is just the highest torque point it makes just as 2000 is the highest point ford makes. However if you do the calculations at both rpms with the torque numbers of the other engine, 1600 and whatever the ford makes VS 2000 and whatever the dodge makes, at both points the dodge has a bigger number.......so deduction tells me that if a bigger number means more power then you have now explained why..............325-600 vs 320-560 bigger number still wins....

I may be ignorant and stupid but is there some reason why you don't compare power at like rpms along the two powerbands, other than the outcome is not what you want?

If not, why?
If not, why?

 

Only problem with this statement. Is that the dodge is still making 600lb ft at 2000 rpm. So at 2000 rpm. The cummins will still do more work.

 

But the work required to move the load varies. From a standing start or uphill would require more hp.

 

As a daily driver. The fact that it has more low rpm hp would make the cummins more driveable. A 5 speed transmission would close the gap between the two. I agree though. A 6.0 with a TS is a very good choice.

 

Ok your math plus mine

ford at 2000 rpms=178,343 assuming 560
ford at 1600 rpms=142,675 this is with 560, optimistic

dodge at 2000 rpms=189,490 this is with 595-probably is higher
dodge at 1600 rpms=152,688 assuming 600


Using your formula and comparing like rpms, higher numbers at rpms go to cummins just like 325-600 vs 325-560. But oh no, there is some reason why comparing two engines at like rpms is not a good comparison.

 

Just one more and then I am going to bed. Using your formula and not rounding numbers we have:

325hp@2900rpms=588.5862 tq
this torque converts to a number of 271799.34

325hp@3300rpms=517.24242tq
this torque converts to a number of 271799.34

This is work force in ft-lbs using MI's formula.
Why it seems that 325hp@2900 has the same number as 325hp@3300. What a surprise.

Seems like the only way I have seen to compare the psd engine vs the cummins engine and make the numbers come up in favor of ford is when not comparing equals. What I have been saying all along.

Good night, and remember, 325-600 vs 325-560.........whatever.

 

This is weird ironman. If you compare hp between two engines you do it at peak or at the same rpm but not peak torque. We can figure out how much either makes at 1600 and then how much either makes at 2000. In both cases the cummins makes more. The PSD does make more hp at 2000 than the cummins makes at 1600. But the cummins make more hp at 2000 than the PSD makes at 1600. See how that works. The math is the same for both at their peaks. Below 2900 rpms the cummins makes more hp. I have shown the math for this. If you multiply 588 by 2900 you would get the same answer as 517 by 3300.
If they both make identical hp. Though at different rpms. Which one can produce more hp? If hp is work. And represents how much weight each engine can move in a period of time. If you have a 1 hp engine that spins 1000 rpms and another 1 hp engine that spins 10000. IF both are hooked to a 1 speed transmission. How many feet can they move 3300 pounds in one minute. Is the 10,000 rpm engine gonna move it faster? Or is it gonna have to sacrifice its massive speed for a higher gear?

If you compare the gears for the cummins and the PSD. The PSD has a higher numerical gear. Because it would put less torque to the wheels if it used the same gear. Less torque at the wheels equals slower acceleration. Or the inability to maintain speed when heavily laden.

Some wheel speed calcs. The cummins with the auto puts more force to the ground only in direct drive,its third, or over drive, its fourth. If the PSD was in fourth,its direct drive, or fifth, its od, climbing a very steep grade. The cummins would have an advantage. Better able to resist deceleration. If the TS shifts down to third and the cummins holds its direct drive, the equivalent to the TS' fourth. Then the cummins will be going faster. More wheel speed. The TS max wheel speed at 3300 rpm in third is 522 rpms, about 50 mph by my simple calculations it could go faster but I just figured it at peak hp for simplicity. The cummins at 2900 in direct has a max 707, about 66 mph by my simple calculations it could go faster but this is at peak hp. Why would the TS have to downshift first? Because it has less torque at the wheels in direct drive than the cummins does. There is usually enough torque in either of these gears to maintain speed up almost any grade, without shifting down into second, on most public highways. So I will leave those figures out. The PSD will go faster in second than the cummins can. More max wheel rpms.

At 2000 rpms in first the PSD auto has 158 rpms to the wheel per minute. 199 for the cummins. Higher wheel speed. At 2000 rpms the cummins has higher wheel speed in all gears with its auto. Why? It has more torque so can use a taller gear. The higher the rpm torque the shorter the gear you must use to get good launch and driveability. If both trucks were going down the highway at 2000 rpms in od. The cummins would actually be going faster. Its just how its geared. Not superior or inferior. Just more torque available so you dont need all those rpms to get the work done. 2000 is a very comfortable cruising rpm for either. Looks like about 65mph for the cummins. The PSD would need about 2050 rpm. Difference in gearing. At this rpm the cummins is capable of producing more hp than a PSD if needed. Not much but a little.

Wow I didnt notice the jump to second for the cummins auto. Holy smokes. Its lower than the ts' third. First gear is a little higher than ts second. No wonder it gets smoked. It really doesnt have much gearing to work with.

That engine gale banks used made a whole lotta torque.
But MI. It can do more work. At all rpms below 2900.

 

Mr. Spencer, good question. I'm glad you asked. Here is why:

Both trucks are moving at the same speed. That speed is 2192 rpms of the transaxle for the entire scenario. We assume each has the same rear-end and wheel sized. Now, at that transaxle speed, the Cummins engine is turning 1600 rpm, and the Ford engine is turning 1560 rpm.

What happens is that their trailers are empty. They both have reserve torque. Weight is added. Each driver must mash the gas pedal down to maintaint the exact same speed. Eventually, the Ford runs out of reserve first, and must downshift. But it must maintain speed if it can. It can. It drops from 5th to 4th gear. The transaxle is STILL turning 2192 rpm, but now the engine is reving higher ... at 2192 rpm (4th gear is a 1:1 ratio). Now both trucks are still rolling ... still at 2192 transaxle rpm.

We continue adding weight to the trailer until the next truck must downshift to maintain speed. At each shift the Dodge has a narrow margin of Torque reserve, and at each shift the Ford has a larger margin of Torque reserve. Eventually the Dodge must shift twice in a row, because it is failing to shift in such a way as to get more torque margin than the Ford. Finally the Dodge redlines ... and it must then back off and slow down.

At the end ... the Ford is still crusing at 2192 transaxle rpms ... in 3rd gear. When the Dodge had to downshift to 3rd gear, it lost it .... and redlined.

Pick ANY starting RPM or speed for Dodge. ANY. I will go through the same shifting math for you. The FORD will be able to maintain speed for the tow-load ... and the Dodge will be forced to redline eventually ... ALWAYS.

This is because the complete and total integrated area under the torque curve from IDLE rpm to STALL rpm is GREATER for the PSD than for the Cummins. No transmission in the world will help Cummins out of that pickle.

I'm trying to be as straightforward as I can, and I'm honestly trying to help you understand what is going on here. Does that explanation help?

Sincerely,
The Ironman

 

Mr. Spencer,

A P.S. on that. If you have each engine going at the same RPM to compare them ... you are not able to compare them. Why? Because if they are both at the same engine rpm ... then they will ALWAYS be at different true speeds. The true comparison is always done at the same identical speeds ... which is the transaxle rpm (assuming they both have the same ratio rear differential and wheel size, of course).

I didn't quite make this point in the post above. Does that help?

Sincerely,
Mr. Ironman

 

I think we're all a little dumber for having read this thread!!!

 

Heretic, I considered for a moment assuming the Cummins had a perfectly flat torque (which it does not). We can go back and do the analysis, and you can tweak up several of those 500 number to 600 or near 600. The final outcome will NOT change. Because the PSD v-engine always has more top-end RPM to keep reaching into ... it will keep downshifting ... until the Cummins cannot out-downshift the PSD.

The Cummins will redline, and fall back.

We can pick any speed. The truck can be going 30 mph or 50 mph or 80 mph. You pick the speed. They start running across the flats together, empty trailers. We start plopping in weights. The Ford will be the first to downshift at the lower speeds (Cummins has more low-end torque, remember). There may be some scenarios in which the Cummins may downshift first, like the 80 mph scenario. In that case, there will likely only ever be one downshift ... from Cummins ... and that's the end. For the lower starting speeds, you will go through multiple downshifts as we saw .... until finally the Cummins cannot rev HIGH enough to maintain a huge weight in it's trailer, that the PSD is able to handle.

Now, Heretic, especially for you, I want to point out that ALL of this is due to the nature of the V-engine characteristics of the PSD. I would wager that if we did this analysis with the C7 Cat and the Cummins ... that would be a much closer competition.

I'm trying to explain this as clearly as possible. I hope that helps.

Sincerely,
Mr. Ironman

 

Heretic. In our scenario, instead of adding weights to the trailer ... it would have been EXACTLY the same to turn a magic crank and start tilting the salt-flats up to a certain angle which equals that tow-load.

The key is that all vehicles don't put out their max torque or HP at a given rpm. It is a partial torque or HP. As you add bags of concrete or something to the vehicle ... you press down the gas to maintain the same rpm. And the actual torque output increases to maintain that rpm. Eventually you reach the max Torque (as published in the curves) for that engine rpm.

At that moment ... if you add so much as another feather ... that engine MUST back off in RPM until it finds a TorqueXRPM combination which can handle the load ... OR .... lug all the way down to idle and quit. That latter can possibly happen with some other types of engines (not internal-combustion).

BUt ... bags of cement ... or tilting the ground underneath ... same thing. No difference.

Sincerely,
The Ironman

 

Here, I think we can agree, if I may define more precisely what you might mean. In our scenario, the PSD had to downshift first. The Cummins did not. So, if by driveability you mean that you have to downshift less ... under certain heavily-loaded scenarios ... the YES .... THE CUMMINS IS MORE "DRIVEABLE". And in our scenario, if the load gets to a point where the PSD must downshift ... and the load and speed requirement stay that way ... then sure ... the Cummins will continue in 5th gear ... and the PSD will continue in 4th gear .... forever.

So, you have a completely valid point. But eventually, however, if that load kept increasing (say .... for that load, we now encounter a very steep hill) ... then both engines will start downshifting. Eventually, if the hill is steep enough, the PSD will keep chugging, and the Cummins will fall back in the to-be-passed lane up the mountain.

By my analysis, PSD's should be awesome hill-climbers. They will downshift before a Cummins ... but can handle tougher hills.

Am I being fair in this analysis?

Sincerely,
Mr. Ironman