Tractor classification — HP vs torque

[LouNY]

Actually.....all else being equal....they will pull and work the same.

But odds are if one is 77cu in and another is over 100 cu in they are probably different size machines.

Put those two engines in the SAME or similar tractors (weight, tire size, traction) and the results will be the same.

I doubt it, I would expect the larger engine to have a better working torque curve and the ability to lug and pull when the smaller displacement will bog down and stall out.

 

[LD1]

I doubt it, I would expect the larger engine to have a better working torque curve and the ability to lug and pull when the smaller displacement will bog down and stall out.

I'd expect the torque curves to be similar in respect to their peak. IE: percent torque rise vs RPM.

In other words.....if RPM drop 10% and torque rise is 15%....I'd expect a similar curve profile for both engines....

For example....kubota D1105 (68CI 25hp engine) vs kubota D1705 (100CI 25hp engine). These are used in the B2601 and L2501. BOTH the same HP spec

The B2601 engine is rated at 25hp/3000RPM and peak torque of 52ft-lbs at 2200rpm
The L2501 engine is rated at 25hp/2200rpm and peak torque of 72ft-lbs at 1500RPM.

Both engines have the peak torque occurring at ~70% of rated (max) engine speed
While operating at 70% of max engine speed (where peak torque is) BOTH engines are still producing ~20-21HP.

While operating at max (rated) engine speed....the B2601 retains 85% of its peak torque #...which puts it at 44ft-lbs. The L2501 retains 81% which puts it at 59ft/lbs

At ~60% the rated engine speed.....
The B2601 engine @ 1800rpm is making 52 ft-lbs and 18HP
The L2501 engine @ 1400rpm is making 70ft/lbs and 18HP.

Look at the graphs.....compare the numbers. YES, the L2501 engine produces more torque. But the 2601 can match the work load by making more RPM's. Everyone seems to forget that you can MULTIPLY torque through gearing. But you CANNOT change horsepower through gearing.

To put it quite simply.....The L2501 makes more torque.....but the B2601 makes proportionally more RPM's. All you gotta do is gear them equivalently and voila.....darn near identical curves.

 

[Chewwy]

Every tractor I have ever driven, when in its lowest gear range and lowest axle range, will spin its tires and NEVER stall out.

Yes, you can make them stall, but only by either intentionally doing so or ignorantly doing so.

 

[WinterDeere]

The guv’ment, in its infinite wisdom, decreed 25 HP was the cutoff for their emissions mandate…

I could create an absurd argument that, if one was to take the CASE steam tractor from the video, scale it down to 25 HP, the torque created by that particular engine would vastly outpace any modern CUT…

The government used the most sensible easily quantified metric on fuel consumption. There's a given amount of energy in a gallon or cubic foot of fuel, and thus rate of fuel usage is linked directly to horsepower through net efficiency. Since all manufacturers aim to maximize efficiency for a given engine type, and because emissions are also related directly to fuel consumption for a given engine type, horsepower was the most sensible and simple metric to use for setting a threshold.

 

[LouNY]

Actually.....all else being equal....they will pull and work the same.

But odds are if one is 77cu in and another is over 100 cu in they are probably different size machines.

Put those two engines in the SAME or similar tractors (weight, tire size, traction) and the results will be the same.

They may by your manipulation of numbers. But, from my seat of the pants from quite a few years of tractors and trucks working them, especially with them being geared transmissions under load the larger engines with similar or even less HP all seemed work better in the fields under normal varying conditions. Most of our operations are in the 3-5 mph range with tillage and planting being closer to 3mph. Mainly because we work quite stoney ground and faster speeds in stones just means more down time from broken parts and wrenching. Mowing is done faster usually and tedding and raking a bit faster. More user friendly torque is what makes for nice smooth operation, I have no use for wound up bumble bee engines.
I can sit all day behind a large engine at 1400-1600 rpm and enjoy it much more then an engine at 2400- 2800 rpm.

 

[finn1]

Both the engine rated at 3200 rpm and the one rated at 2100 rpm can have torque rise.

Correct