why horsepower

[s219]

If someone wanted to hot rod the L2501, all they would need to do is raise the RPM limiter and then you'd have the same performance range as the old 34HP L3400. But you won't notice a difference at the lower RPMs, and for most tractor uses that's where we operate so you already have the effective 34HP engine there. That is what makes the L2501 such a good package and deal, as you're getting a 34HP tractor for most purposes.

If you do raise the RPM limiter then you will need to either change the PTO gearing (so it still hits 540rpm at your desired engine RPM) or just operate the PTO at the existing lower RPM set point and live with lower PTO HP.

Knowing how I operate my L3200 and the RPM ranges I normally use, I wouldn't change the L2501 one bit. That tractor can do everything my L3200 can do for ground engagement, as good or better than the L3200. The only advantage I see from the L3200 is PTO power output, which is only a factor when running my wood chipper. For everything else I do the L2501 would be as good or better. The 7HP advantage of the L3200 is all on paper for most practical purposes, and should not be allowed to confuse the situation.

 

[art]

You are correct that torque is very important in your equation. Playing with the dyno and tractor pulling farmers it has been very interesting for what we have seen. Years ago there were several manufacturers that were using air cooled engines. What we learned was they were great for fuel economy but on our hills customers often complained that they had to shift down so much while climbing hills pulling a load. We found that by adding more fuel to increase the horsepower to allow them to climb gave us heating issues. The fans to cool them where run from the engine and as the rpm went down under load so did the fan speed which caused to problem. We did add extra electric fans while they pulled the tractors to help with the cooling.
Water cooled engines didn't have those issues! There were makes that had more torque with IH at the time being one of the leaders with models like the 1086 that was rated at 130 horsepower but at 80% of Rpm it was 135 horsepower and you could make it even stronger!! They would climb hills and you wouldn't need to worry about shifting down under load. We saw other tractors that if they were 98 horsepower we could open up the pumps and they would only go to 120 hp but when you tightened them down they instantly started loosing horsepower. There were still engine designs that could not handle the higher torque and would blow under high torque and fuel conditions. Torque is staying ability when you hit a load on the engine and it is important for field work but not so much loader work. Today many makes will call it a power bulge and today we can see them gain far more then the mechanical pump on the 1086 could handle and often they are in close to a 40% bulge in power with the electronic injection systems.

 

[Texasmark]

Torque is "potential energy" the twisting moment of inertia. Horsepower is energy consumption. Simple formula for HP = [Torque (ft-lbs) x RPMS]/5252. Or you can take horses and weights of a certain size, lifted a certain distance, in a certain amount of time.

Consumption of energy is "Work". Work is what the plow does to the soil consuming the energy in the process and converting it to a different form.

Tractors and large "mass" engines run low rpms which translates to long life when one can tolerate the extra weight. When one can't one has to revert to upping the rpms.....like the Liberty Ships of WWII ran in the hundreds of rpms while your model airplane engine may be running at 20k rpm.

Mercury Marine boasted of the first outboard engine at 1 cu in per HP back in the '60's, like with their Merc. 1000, 100 hp at 99 cu. in., but they had to do it at 6k rpms, while OMC was running large cube engines at 4500 rpms. OMC advantage there was that at the lower rpms a larger diameter prop at shallower pitch developed more "thrust" in the water and pushed heavy loads better for a given rpm.

On measuring what a tractor can do, the easiest method is a dynamometer whereby a load is placed on the PTO shaft and the HP is calculated....reason you see PTO hp posted......unless you consult the U of Nebraska tractor testing where they have the time/equipment/money to do the full blown shebang.

This is sort of the way I remember it.

 

[art]

Anyone recall drawbar horsepower?? It was delegated to the pulling capabilities.

Drawbar was a interesting concept as a measure for horsepower and before the PTO was being used to power implements it was the only standard they had. Good or bad if someone didn't ballast right that was a bigger concern then actual horsepower! They did use that into the fifties before PTO took over completely. The pto is a good constant measure and it is very interesting to be able to crank a dyno down on a tractor to the recommended RPM and draw a load on the engine to see if you have the horsepower. Now to give it extra load to see if the horsepower dies or goes up that is torque if the horsepower is going up!

 

[ericm979]

the 2501 uses mechanical injection.

Kubota may have limited it's power by using smaller injectors or a different pump than the older higher HP model the engine came from in addition to limiting the rpm. Or they may have only limited the rpm in the governor. Raising the rpm could add power but now the PTO will be turning too fast at the new higher hp peak and the wheel gearing will be high. So you're unlikely to get much more power PTO speed and you'll be plowing fast to get on the new higher power peak.

You'd need an expert in mechanical injection modification to figure out what Kubota did and use parts from other models to undo it. Once that's been figured out it may be affordable but paying for the research might be costly.

 

[TheMadOne]

the 2501 uses mechanical injection.

Kubota may have limited it's power by using smaller injectors or a different pump than the older higher HP model the engine came from in addition to limiting the rpm. Or they may have only limited the rpm in the governor. Raising the rpm could add power but now the PTO will be turning too fast at the new higher hp peak and the wheel gearing will be high. So you're unlikely to get much more power PTO speed and you'll be plowing fast to get on the new higher power peak.

You'd need an expert in mechanical injection modification to figure out what Kubota did and use parts from other models to undo it. Once that's been figured out it may be affordable but paying for the research might be costly.

No. The L2501 uses the same direct injection engine design as the L3301 and L3901, and is computer controlled, making any changes much more complex than on a mechanical injection engine. It likely can't be "turned up" easily even with a chip as it looks like a different cam was used, as the displacement and stroke are both smaller on the L2501 than it's bigger brothers.

 

[CobyRupert]

Torque, (horse)power, work, energy, force...
Some of these terms are getting jumbled here.
Perhaps a bit off subject, but going back to basics. If you really want to understand these terms on a deep personal level, ride your 10 speed bike up a hill that takes 1 minute. Takes the same Energy no matter how fast or slow you do it. But you have to output 2x the horsepower if you want to do it in 1/2 the time. Or 1/2 the horsepower if you take twice as long. Same Energy used in all cases. Same work done. Horsepower is just how fast (time-wise) you were able to output the energy required to do the work.
Ok? Now what does this have to do with torque?
Now..realizing you have 10 gears and sticking with the 1 minute climb time (I.e thus we are outputting same horsepower no matter what gear): The torque required is a trade off with your rpms (a function of your gear selection) as HP formulas above say. This is where the reality hits the fan. Pick a high gear if you want slow pedal rpms, but each pedal turn may require so much “torquing” you may stall from lack of strength (torque). Or pick the lowest gear and it will feel easiest (low torque) but you’ll have to spin (rpm) your legs so fast to keep the 1 minute pace (and constant HP) that you’ll overheat.
It’s always a balance of using the right torque and rpms (Power- torque-rpm curve) and gearing to the characteristics of motor being used which gives you the best horsepower....which gives you how fast you can do the task (work).
2cents.

 

[1930]

Torque, (horse)power, work, energy, force...
Some of these terms are getting jumbled here.
Perhaps a bit off subject, but going back to basics. If you really want to understand these terms on a deep personal level, ride your 10 speed bike up a hill that takes 1 minute. Takes the same Energy no matter how fast or slow you do it. But you have to output 2x the horsepower if you want to do it in 1/2 the time. Or 1/2 the horsepower if you take twice as long. Same Energy used in all cases. Same work done. Horsepower is just how fast (time-wise) you were able to output the energy required to do the work.
Ok? Now what does this have to do with torque?
Now..realizing you have 10 gears and sticking with the 1 minute climb time (I.e thus we are outputting same horsepower no matter what gear): The torque required is a trade off with your rpms (a function of your gear selection) as HP formulas above say. This is where the reality hits the fan. Pick a high gear if you want slow pedal rpms, but each pedal turn may require so much “torquing” you may stall from lack of strength (torque). Or pick the lowest gear and it will feel easiest (low torque) but you’ll have to spin (rpm) your legs so fast to keep the 1 minute pace (and constant HP) that you’ll overheat.
It’s always a balance of using the right torque and rpms (Power- torque-rpm curve) and gearing to the characteristics of motor being used which gives you the best horsepower....which gives you how fast you can do the task (work).
2cents.

Good analogy

 

[1930]

Good video KUBOTA L251 VS L391 - How does Horsepower affect your loader? - TMT - YouTube

 

[Chris from Ontario]

Torque is simply a force that has no movement. RPM only describes speed. Speed at a given torque, combined, is horsepower. Horsepower is what does work. Work is accomplished by rotation that is backed up with torque.

So, if you have a rotating shaft, how fast is it going and how much force is trying to keep it turning?

If you put an arm on the shaft that was one foot long, and it was able to lift a 10 lb weight out at the end of the arm, the force would be 10 ft lbs., or 10 ft lbs of torque required to lift the weight. How fast it lifted the weight, combined with how much weight, would add up to horsepower.

Hi torque engines run slower for a given horsepower. Engines that turn twice as fast, can be geared two-to-one and provide twice as much torque. So a small engine can provide a lot of torque if the power is fed through a transmission to match the engine to the load, as in cars.

However, it's impractical for a tractor engine to be running at 10,000 RPM all the time, and geared way down to a useful RPM to multiply the torque. Just as it's impractical for a chain saw to weight 500 lbs and be geared way up from 1,000 RPM to match the required speed.

Smaller engines can be made to put out a lot of horsepower, but they are harder to control and cool and make last a long time under those conditions. Each machine needs the appropriate sized engine, not just for the horsepower it requires, but for the practicality of carrying that engine around (tractor, car, motorcycle). Stationary generator engines can be heavy, airplane engines must be light. Tractors need weight to engage the ground and remain stable, locomotives need weight and must run a very long time, Chainsaws must be light and powerful, but don't run many hours, etc, etc.

When you see a tractor/trailer rig pulling a grade, it's the horsepower that's doing the work. But the engine is very heavy and slow turning. This means it has high torque and low RPM, for it's rated horsepower, is durable and the transmission can be a simple design to match the engine to the wheels. It makes more sense than having 100 chain saw engines hooked up to the wheels, but the horsepower is the same. And the speed up the grade is the same because it's the horsepower that does the work. Torque is only one part of horsepower.

Raspy, that is one fantastic and simple way of explaining torque and horsepower. Thank you very much for that!