Why HP?

[crabjoe]

I'm just wondering out loud here....

These are tractors we're looking and and being that they built for work, why do OEMs seem to only post HP numbers? Torque is power, so what we really need to see is how much torque the motor produces and at what RPMs.

HP is just a number based on torque and rpms anyways.

I wish these manufacturers would start publishing torque curves for the motors used in their tractors. If we could see them, then we would have a better idea on why some lower HP tractors are rated for more lifting and pulling; even being able to pull it's own weight around.

 

[LAWALLSTRACTOR]

HP is something the average public thinks they understand, so it is used the sell the tractors. Most of the public doesn't understand that lots of HP in a little tractor doesn't necessarily get the job done.

 

[art]

Joe, there is so much that goes into it and torque is an important part of the power on the tractors. Good torque goes along way towards holding engine speed under varying loads.
The weight, and where it is positioned makes a big difference in performance while pulling loads or climbing hills or going down them!

There is nothing better then a good performing tractor, horsepower , torque and weight distribution are good starting points but they can not over come a bad set of tires for pulling!

We used to use a older cadet with a hydro to pull dead tractors into our shop. It was 14 hosepower with a hydro, and with a little coaching it pulled 15,000lb tractors all day long!

 

[Patches]

Kioti used to spec torque and horsepower numbers for their various engines on their web site and in the specific brouchers in graph form. I haven't checked their web site for some time, so don't take my word for it

 

[dfkrug]

HP is just a number based on torque and rpms anyways.

Well, the torque an engine produces can be multiplied (by gearing); the
hp it produces can not. HP is a measure of work. Torque is a measure
of force. A force that causes no motion, produces no work.

I wish manufacturers would be more up front about publishing WEIGHTs.
One has to dig deep into specs to find this out, for tractors or other
vehicles. All the multiplied torque in the world can only move something
if it has TRACTION, a function of weight and friction.

 

[GaryCrowell]

Torque is power, so what we really need to see is how much torque the motor produces and at what RPMs.

Sorry, but you're wrong. Torque is not power, torque is a force. HorsePOWER is power, specifically it's torque multiplied by RPM divided by 5252. It's a measurement of the rate of doing work. The reason you see equipment advertised by horsepower is because horsepower is what matters in determining how much work the engine is capable of. Torque is just a component of horsepower and is a "nice to know" number but really doesn't have any bearing upon the capabilities of the tractor. An engine that produces lots of torque down low will make it's horsepower at a lower RPM than an engine with lower torque output. In other words, the lower torque engine will have to turn faster to make the same horsepower BUT it is capable of doing exactly the same amount of work as the lower RPM/higher torque motor. As an example think of the turbine engine in a M1 abrams tank, it's turning at 10,000-15,000 RPM and produces comparatively little torque but makes gobs of horsepower because of it's RPM, thus resulting in some pretty amazing performance out of that heavy tank. Older diesel tank engines produced much more torque but their RPM was low and they were pretty much pigs.

Equipment is advertised by horsepower because the engineers that build them know that it's all that matters. This myth that torque determines performance is something that the old muscle car racers dreamed up based upon their skewed misunderstanding of physics. It's a myth that's become stuck in the minds of a lot of folks but it's wrong. Torque is just a component of horsepower, it's not "torque vs. horsepower". It's like bragging on Aunt Sallie's delicious cake then getting hung up on what type of baking powder powder she used. It really doesn't matter as long as the end result is a good cake.

 

[wkpoor]

Sorry, but you're wrong. Torque is not power, torque is a force. HorsePOWER is power, specifically it's torque multiplied by RPM divided by 5252. It's a measurement of the rate of doing work. The reason you see equipment advertised by horsepower is because horsepower is what matters in determining how much work the engine is capable of. Torque is just a component of horsepower and is a "nice to know" number but really doesn't have any bearing upon the capabilities of the tractor. An engine that produces lots of torque down low will make it's horsepower at a lower RPM than an engine with lower torque output. In other words, the lower torque engine will have to turn faster to make the same horsepower BUT it is capable of doing exactly the same amount of work as the lower RPM/higher torque motor. As an example think of the turbine engine in a M1 abrams tank, it's turning at 10,000-15,000 RPM and produces comparatively little torque but makes gobs of horsepower because of it's RPM, thus resulting in some pretty amazing performance out of that heavy tank. Older diesel tank engines produced much more torque but their RPM was low and they were pretty much pigs.

Equipment is advertised by horsepower because the engineers that build them know that it's all that matters. This myth that torque determines performance is something that the old muscle car racers dreamed up based upon their skewed misunderstanding of physics. It's a myth that's become stuck in the minds of a lot of folks but it's wrong. Torque is just a component of horsepower, it's not "torque vs. horsepower". It's like bragging on Aunt Sallie's delicious cake then getting hung up on what type of baking powder powder she used. It really doesn't matter as long as the end result is a good cake.

Good post and I agree. Now tell me why a 60HP gas tractor doesn't have the power of a 60HP diesel one.

 

[crabjoe]

Sorry, but you're wrong. Torque is not power, torque is a force. HorsePOWER is power, specifically it's torque multiplied by RPM divided by 5252. It's a measurement of the rate of doing work. The reason you see equipment advertised by horsepower is because horsepower is what matters in determining how much work the engine is capable of. Torque is just a component of horsepower and is a "nice to know" number but really doesn't have any bearing upon the capabilities of the tractor. An engine that produces lots of torque down low will make it's horsepower at a lower RPM than an engine with lower torque output. In other words, the lower torque engine will have to turn faster to make the same horsepower BUT it is capable of doing exactly the same amount of work as the lower RPM/higher torque motor. As an example think of the turbine engine in a M1 abrams tank, it's turning at 10,000-15,000 RPM and produces comparatively little torque but makes gobs of horsepower because of it's RPM, thus resulting in some pretty amazing performance out of that heavy tank. Older diesel tank engines produced much more torque but their RPM was low and they were pretty much pigs.

Equipment is advertised by horsepower because the engineers that build them know that it's all that matters. This myth that torque determines performance is something that the old muscle car racers dreamed up based upon their skewed misunderstanding of physics. It's a myth that's become stuck in the minds of a lot of folks but it's wrong. Torque is just a component of horsepower, it's not "torque vs. horsepower". It's like bragging on Aunt Sallie's delicious cake then getting hung up on what type of baking powder powder she used. It really doesn't matter as long as the end result is a good cake.

I agree torque is force (T = Distance * Weight), and I feel that is power. Basically I see Force and Power being the same.

I can not agree HP is power because it's just a number derived from torque and engine speed. Your example of the tanks is really deceiving to me because, logically, it seems gearing can give you speed. And no matter how much engine speed you have, if you don't have enough "Force" to get the weight moving, it ain't moving, regardless of the engine speed.

Years ago, someone explained it to me like this. Torque is power because it's used to move weight, and HP was speed; assuming you had enough torque to move it in the 1st place.

Based on that tank example and what was told to me, the engineers made sure that the M1 had enough torque to be able to move the tank, but put it into a faster spinning motor to get it moving faster. If you think about it, they could have used gearing instead of engine speed to get the old tanks to move faster. I'm guessing they didn't do it for a number a reasons. one being size. It takes less volume to increase engine speed then to add gears; less eight too.

So if HP is just a number derived from T and R, how does it really mean anything other then marketing? HP marketing makes sense, when it was invented, because at that time, people understood how much work 1 horse could do.

BTW how did they ever come up with using 5252 to get HP, why not use 5000 to make it seem as if they were giving more horses?

 

[john_bud]

Good post and I agree. Now tell me why a 60HP gas tractor doesn't have the power of a 60HP diesel one.

I will, if you tell me why you think it doesn't! (Here's a hint -> they are the same)

A diesel will generally "feel" more powerful because it has more torque at a lower RPM. This is not always the case. Old Fords (172 cid 4 cylinder) were available in gas and diesel. Same bore x stroke and # of cylinders. Guess what? The GAS engine had more torque and more HP at EVERY rpm. That is a historical fact that you can easily verify.

On your question, if you set the rpm's of your theoretical 60hp engines so that both are at the point where they make 60 hp, you can put them on a dyno and will get 60 hp. The gas engine may have to be rev'ed up higher than the diesel engine, so if you only test them at identical RPM's the diesel will make a better showing.

 

[mike194]

power = the amount of work done or energy transferred per unit of time


torque has nothing to do with time a five pound weight sittting on a one foot wrench is 5 ft/lbs even if it is sitting on there for an hour

 

[GaryCrowell]

I agree torque is force (T = Distance * Weight), and I feel that is power. Basically I see Force and Power being the same.

I can not agree HP is power because it's just a number derived from torque and engine speed. Your example of the tanks is really deceiving to me because, logically, it seems gearing can give you speed. And no matter how much engine speed you have, if you don't have enough "Force" to get the weight moving, it ain't moving, regardless of the engine speed.
.........

BTW how did they ever come up with using 5252 to get HP, why not use 5000 to make it seem as if they were giving more horses?

Torque and horsepower have strict definitions in physics. When you state that torque is power, strictly speaking by the physics book you're wrong, it just isn't so. Horsepower is one way power is measured, another way is by the Watt. Think of the 100 watt light bulb in your house, that's how much power it consumes. An engine's output could just as easily be expressed in Kilowatts (1000 watts) by juggling the units around. If you look on the ID tag of most diesel engines they'll have the power stated in Kilowatts also. Horsepower is gradually being phased out in favor of Watts since horsepower is considered kind of an archaic unit. As for where the term "horsepower" came from, here's what wikipedia says:

"The term "horsepower" was coined by the engineer James Watt (1736 to 1819) in 1782 while working in the performance of steam engines. This occurred while using a mine pony to lift coal out of a coal mine. He conceived the idea of defining the power exerted by these animals to accomplish this work. He found that, on the average, a mine pony could pull (lift by means of a pulley) 22,000 foot-pounds per minute. Rather than call this "pony" power, he increased these test results by 50 percent, and called it horsepower i.e. 33,000 foot-pounds of work per minute."


The number 5252 is a conversion factor used to convert the rotational speed of an engine (RPM) to straight line speed. Since Mr. Watt decided that a unit of horsepower is 33,000 lb. ft/min, to get the conversion factor you take 33,000 and divide it by 2 times the numerical value of Pi, which is 3.1416. The result is 5252. It's just a conversion number like dividing by 3 if you want to know how many yards are in 100 ft.

Years ago, someone explained it to me like this. Torque is power because it's used to move weight, and HP was speed; assuming you had enough torque to move it in the 1st place.

That's the old hot rodder's explanation of why a big block motor will typically get off the line quicker than a small block, they justified it by the big block's having more torque. It's wrong, but that doesn't seem to get in the way of a good story. The real reason is because the big block produces more Horsepower at lower engine speeds (because it has more torque, since torque is a component of horsepower), but torque in and of itself can't, by definition, do anything. Only when there's movement associated with the torque can it do work. You have to have torque to have horsepower, if you have 0 torque you also have 0 horsepower, just as if you have 0 RPM you have 0 horsepower.

It gets confusing because so much of the common perception about torque and horsepower is wrong. Many old timers have drawn conclusions based upon their perceptions rather than what's really happening, i.e. "My tractor's not got much horsepower but a bunch of torque and it can pull a house, so torque must mean more power". In reality it doesn't take much power to pull a house, it just takes a lot of mechanical advantage (leverage), which can be multiplied through gearing, and a means of maintaining traction. You won't pull the house very quickly without a lot of horsepower, but to just get it to move you could use a hamster in a wheel as long as you run the power through the proper gears and get some traction.


Give me a lever long enough and a fulcrum on which to place it, and I shall move the world. -Archimedes

 

[Rara Avis]

I'm just wondering out loud here....

QUOTE]

Well it's because if the fuel runs out that is what we will be back to using...HORSE POWER...

 

[wkpoor]

I read somewhere what the opposite ends of the spectrum are for torque in a machine.
A water wheel produces the most torque for its RPM
A turbine engine produces the least. Thats not to say a water wheel has more torque, just that the ratio of torque to RPM.
Since HP is derived from torque and RPM obviously some engines will apply more force at lower speeds than others. Steam power produces alot of torque but isn't practical. Diesels produce more torque for a givin RPM therefore make better powerplants for tractors. It seems that an engine with greater torque at lower speeds is more efficient for moving objects.