Tractor classification — HP vs torque

[finn1]

Torque rise today is usually a lot more than 15%. Nebraska changed their testing some in the early 1990s and started to publish engine torque numbers and torque rise between rated speed and peak torque. I'll pick on some tractors I've run that have been tested at Nebraska and have figures available for peak torque and torque rise. They are definitely not high power by modern standards but the New Holland would have been a pretty potent tractor back in those days and the others' size would have put them right in the middle of the ag market back then, so not completely inappropriate.

- Deere 5075E (Final Tier 4, common-rail turbocharged and intercooled): Rated speed 2100 RPM. Peak torque 209 ft-lb at 1249 RPM, torque rise 31.6%
- Deere 5083E: (Tier 3, mechanical injection, turbocharged): Rated speed 2400 RPM. Peak torque 204 ft-lb at 1499 RPM, torque rise 41.3%
- Deere 5410: (Tier 1, mechanical injection, naturally aspirated): Rated speed 2400 RPM. Peak torque 204 ft-lb at 1094 RPM, torque rise 42.5%
- New Holland T6030 (Tier 3, mechanical injection, turbocharged and intercooled): Rated speed 2200 RPM. Peak torque 422 ft-lb at 905 RPM, torque rise 63.6%.


Going back to the original question as to why engines are rated according to HP rather than torque is because horsepower is what accomplishes work. You can have a high-torque engine that turns slowly or a low-torque engine spinning fast and both will do the same amount of work. For example, CNH's Workmaster 70/Farmall 70A are competitors to the Deere 5075E above and they take the opposite strategy with engines:

- Deere 5075E (FT4): 179 cid turbocharged (17.7 PSI), intercooled, common-rail three-cylinder. Rated speed 2100 RPM, redlines at 2200 RPM. Produced 64.2 PTO HP at 540 PTO RPM (2083 engine RPM), 209 ft-lb torque at 1249 RPM, torque rise of 31.6%. Fuel efficiency 14.2 HP-hr/gallon.
- CIH Farmall 70A (2019): 136 cid turbocharged (18.2 PSI), intercooled, common-rail three-cylinder. Rated speed 2600 RPM, redlines at 2800 RPM. Produced 63.5 PTO HP at 540 PTO RPM (2575 engine RPM), 167 ft-lb peak torque at 1798 RPM, torque rise of 29.2%. Fuel efficiency 13.8 HP-hr/gallon.

The much smaller engine with a much higher operating speed has noticeably less torque but makes almost exactly the same PTO power, has a similar torque rise, uses about the same turbocharger boost, and even has very similar fuel efficiency. I would thus expect very little difference in performance between the two engines despite the torque difference.

I’m just going by what I remember from setting master pumps on an engine dyno in the mid 70s. That’s a long time ago, and I don’t know how well a pto dyno or chassis rolls correlate to actual engine crankshaft power readings.

I do know that when I worked at Ford Tractor when they were in Troy, Mi in about 1976, the chassis dyno accuracy was something of a joke.

Also, I don’t remember for sure, but I think the torque numbers on the sales curves, which were used for the master pump settings. were limited to a large extent by the drivetrain capability.
We were using mostly Ambac model 100 pumps at the time, and they weren’t the most capable fuel systems. The Bosch VA and VE pumps were similar In capability. Modern common rail systems aren’t limited in fuel delivery (cc/stroke) by mechanical realities of a speed dependent rotating pump cam, and driveline capabilities have undoubtedly improved.

One other thing about the Nebraska tests, is those fully dressed engines all ran mechanical fans, and a fan curve is typically an exponential shape. That is, it pulls a lot more power as speed increases, which alters the apparent torque rise numbers. Engine manufacturers typically don’t include the fan in gross power or torque numbers since the fan is application specific, while a given engine can go in literally dozens of applications.

In summary, the Nebraska tests are valid for a given tractor, and represent power and torque rise in a given machine, but the numbers will be significantly different from what an engine manufacturer publishes for that same engine because of installation compromises and conditions, as well as the inherent inaccuracy of the Nebraska test methodology.

 

[LD1]

This HP vs Torque comes up often. And its surprising how some seem to not understand how the two are directly related. Or equally surprising how some think HP is a more meaningless number than torque.

A few people got the answer right.....And it really is that torque at the engine dont really matter...it can be changed to whatever you need by gearing. HP will not change with gearing.

Torque is just a number of force. HP is how fast torque can be applied....IE: how long it takes to get work done.

Tractors are pieces of equipment to do work around a farm. Going from a 100hp machine to a 200hp machine will tell you that the upgrade should allow you to do twice the work in the same amount of time. OR the same amount of work in half the time. How do you compare that with a static torque number.

 

[LouNY]

To me torque is the more important factor. Torque is what lets me maintain a fairly constant ground speed while running a forage harvester, mowing in various crop conditions, performing tillage at a constant depth in varying field conditions. My rpm will stay more constant when it's needed to for spraying and broadcast spreading. When I bring the engine speed up to my pto rpm desired and start across or around a field I want my engine rpm/ pto rpm staying constant I can vary my travel speed via my gears if I need to but I want a constant pto rpm often.

 

[LD1]

To me torque is the more important factor. Torque is what lets me maintain a fairly constant ground speed while running a forage harvester, mowing in various crop conditions, performing tillage at a constant depth in varying field conditions. My rpm will stay more constant when it's needed to for spraying and broadcast spreading. When I bring the engine speed up to my pto rpm desired and start across or around a field I want my engine rpm/ pto rpm staying constant I can vary my travel speed via my gears if I need to but I want a constant pto rpm often.

What you describe is horsepower whether you or others want to admit it or not.

You talk about torque and speed, or torque and RPM.....which is EXACTLY what HP is.

 

[LouNY]

No, I'm not the torque curve or flatness of it is what enables smooth operation.
The DEFININTION of HP is Speed x Torque I'm looking for and using a flat torque curve to do the work.
With my rpm remaining constant it is the TORQUE that is performing the work.

 

[Cougsfan]

I think it is just because most people are conditioned to think in terms of horsepower. 45 hp is a relatable term to most people while 38 ft lb of torque comes across as an ambiguous figure. Knowing either max torque or max hp is limited in what it tells you. What is really telling is a torque curve (How much torque at various rpms) A long relatively flat curve is ideal in a tractor.

Just an interesting side note: A steam engine develops max torque at 0 RPM

 

[rScotty]

No, I'm not the torque curve or flatness of it is what enables smooth operation.
The DEFININTION of HP is Speed x Torque I'm looking for and using a flat torque curve to do the work.
With my rpm remaining constant it is the TORQUE that is performing the work.

I gotta go with LouNY on this one. He is holding RPM constant and allowing TORQUE to vary. HP becomes a derivative by definition in the same way that the louder sound created is also a derivative value. Neither sound nor HP are causes. Both are effects, not causes.
rScotty

 

[LD1]

No, I'm not the torque curve or flatness of it is what enables smooth operation.
The DEFININTION of HP is Speed x Torque I'm looking for and using a flat torque curve to do the work.
With my rpm remaining constant it is the TORQUE that is performing the work.

Torque is just a force. A force that does work. HP adds the time element to how long it will take to get the work done.

IF you pick a specific RPM.....and want the most torque.....it will also be the one with the most horsepower.

If you want to maintain torque as RPM's change or drop.....its ALSO maintaining HP better....IE: area under the curve on a HP graph.


I can apply MORE torque with a 2' torque wrench than most of our compact tractor engines can. AND.....with proper gearing I can also apply MORE force/do more work than most of them can. But I cannot do it at any rate of speed at all in comparison since our compact tractors are about 100x more powerful than a humans "hprsepower" rating

 

[Hay Dude]

Torque rise today is usually a lot more than 15%. Nebraska changed their testing some in the early 1990s and started to publish engine torque numbers and torque rise between rated speed and peak torque. I'll pick on some tractors I've run that have been tested at Nebraska and have figures available for peak torque and torque rise. They are definitely not high power by modern standards but the New Holland would have been a pretty potent tractor back in those days and the others' size would have put them right in the middle of the ag market back then, so not completely inappropriate.

- Deere 5075E (Final Tier 4, common-rail turbocharged and intercooled): Rated speed 2100 RPM. Peak torque 209 ft-lb at 1249 RPM, torque rise 31.6%
- Deere 5083E: (Tier 3, mechanical injection, turbocharged): Rated speed 2400 RPM. Peak torque 204 ft-lb at 1499 RPM, torque rise 41.3%
- Deere 5410: (Tier 1, mechanical injection, naturally aspirated): Rated speed 2400 RPM. Peak torque 204 ft-lb at 1094 RPM, torque rise 42.5%
- New Holland T6030 (Tier 3, mechanical injection, turbocharged and intercooled): Rated speed 2200 RPM. Peak torque 422 ft-lb at 905 RPM, torque rise 63.6%.


Going back to the original question as to why engines are rated according to HP rather than torque is because horsepower is what accomplishes work. You can have a high-torque engine that turns slowly or a low-torque engine spinning fast and both will do the same amount of work. For example, CNH's Workmaster 70/Farmall 70A are competitors to the Deere 5075E above and they take the opposite strategy with engines:

- Deere 5075E (FT4): 179 cid turbocharged (17.7 PSI), intercooled, common-rail three-cylinder. Rated speed 2100 RPM, redlines at 2200 RPM. Produced 64.2 PTO HP at 540 PTO RPM (2083 engine RPM), 209 ft-lb torque at 1249 RPM, torque rise of 31.6%. Fuel efficiency 14.2 HP-hr/gallon.
- CIH Farmall 70A (2019): 136 cid turbocharged (18.2 PSI), intercooled, common-rail three-cylinder. Rated speed 2600 RPM, redlines at 2800 RPM. Produced 63.5 PTO HP at 540 PTO RPM (2575 engine RPM), 167 ft-lb peak torque at 1798 RPM, torque rise of 29.2%. Fuel efficiency 13.8 HP-hr/gallon.

The much smaller engine with a much higher operating speed has noticeably less torque but makes almost exactly the same PTO power, has a similar torque rise, uses about the same turbocharger boost, and even has very similar fuel efficiency. I would thus expect very little difference in performance between the two engines despite the torque difference.

There would be a performance difference when it comes time to actually do the work. Given proportional sized cooling systems, the larger displacement engine should run cooler. Heat kills engines and bolted-on engine components.
So when the rubber hits the road (or the plow gets dropped into the soil, the bush hog gets pulled through heavy brush) the bigger displacement engine will run cooler and last longer. You can work it harder in the field.

Some things cannot be explained with paper statistics. They just are a certain way a tractor feels when you drive it. In a tractor, I would prefer noticeably more displacement of a bigger engine over a smaller displacement engine, even if the smaller engine had a little more power.

I’m skeptical of these smaller 4-liter-ish, 4 cylinder engines I’m seeing in 100-150HP tractors. I don’t think they are going 10,000 hours. I greatly prefer a 6 cylinder over a 4 cylinder, too. The longer crankshaft and 6 smaller holes firing give me more confidence than a short crank and 4 holes firing.

 

[S854]

IF you pick a specific RPM.....and want the most torque.....it will also be the one with the most horsepower.

If you want to maintain torque as RPM's change or drop.....its ALSO maintaining HP better....IE: area under the curve on a HP graph.

This is a dyno chart of one of the Cat equipped road tractors we have where I work (heavy construction)

I pull double, cement bulk trailers in western Montana… 128,000# give or take…

When I first drove this tractor, and came to “the hill” (6% uphill for a little over a mile), I would start downshifting, four or five gears, to keep the engine between 1,900 - 2,100 rpm which is at the peak of its HP range…

One day I got lazy… ok, I was “experimenting”, I let the engine begin to “lug” … and found the engine would continue to pull hard down to 1,100 rpm… I still needed to downshift a few times, but I didn’t have to keep the engine racing and the tractor/trailer climbed the hill at a greater speed than it would in a lower gear with the engine racing…

Which brings me back to the reason I started this thread… and I STILL can’t wrap my head around why it‘s HP performing the work when, in my experience, I see torque taking over when it comes time to do the heavy lifting…

As was pointed out earlier in the thread, two 25 HP tractors with two different displacements… seems to me the larger of the engines will generate more torque throughout a broader spread…