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Old 09-03-2005, 01:23 PM   #1
Fredrick_NP
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What is the difference between HP and Torque

I googled it to find out, but sites that came up had really complex explanations that I didnt understand.

I always thought HP was the more important spec, but I guess I was wrong.

Also, is 200HP & 205 ft-lbs @4500 RPM a good engine?
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Old 09-03-2005, 08:02 PM   #2
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Re: What is the difference between HP and Torque

Quote:
Originally Posted by Fredrick_NP
I googled it to find out, but sites that came up had really complex explanations that I didnt understand.
I always thought HP was the more important spec, but I guess I was wrong.
As simple as possible,.... HP is a unit of work. Torque is a unit of Force. The more force that can be applied over a given amount of time. the more work (HP). In a sense, Torque and HP are the same thing. However, if more torque can be applied over the same amount of time, more work (HP) can be done.


Quote:
Also, is 200HP & 205 ft-lbs @4500 RPM a good engine?
"Good" engine? Don't know. Depends upon what you want it to do. Engines can be designed to produce lots of different torque at many different RPM points. It depends upon what you want that engine to do and at what RPM.

Jim
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Old 09-03-2005, 11:00 PM   #3
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Re: What is the difference between HP and Torque

you need torque to get your vehicle moving and up to speed and horsepower to keep it going once you get there
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Old 09-03-2005, 11:46 PM   #4
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Re: Re: What is the difference between HP and Torque

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you need torque to get your vehicle moving and up to speed and horsepower to keep it going once you get there

???

No.. You need HP to do either. The more HP the better it can do either. The only difference is the final drive ratios you need and the point in RPM that you engine will pull best.

Again. HP is work... To do any work... accelerate a mass, keep a mass rolling and overcoming air resistance and wheel/road resistance requires HP. Torque is simply a measure of force that can be mapped against the RPM so you can determine WHERE in RPM that engine performs best.

HP = TORQUE x RPM / 5252. See?

Jim
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Last edited by sracing; 09-04-2005 at 02:21 PM.
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Old 09-04-2005, 12:12 AM   #5
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Re: What is the difference between HP and Torque

Torque is actually a static measurement like you create with a wrench. Although you are moving, the point at which you cant turn anymore is the point where the bolt is giving back the same amount of torque force that your arms can generate. HP is like a swinging hammer. A 2-lb hammer can make a 100-lb impact when moving fast enough.

In an engine, torque is a bit abstract, but if an engine makes 100 ft-lbs, that means it would require 100 ft-lbs to stop it. Its a bit abstract because a stopped engine makes no torque but maybe that can illustrate it. HP is technically defined as torque over time. Going back to the hammer analogy, a resting hammer does no work, but get it swinging and it does work. If you start swinging it around in a circle it can do some damage. The faster you swing it, the more energy it has and therefore can do more damage.

Engines produce torque. As a function of their speed, torque produces HP.
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Old 09-04-2005, 01:43 PM   #6
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Re: What is the difference between HP and Torque

horsepower is like a measurement of the "pulling force" at a certain speed-RPM in this case lets use this example; a car with 250bhp (brake horsepower) means it can pull the same amount of weight (?) as 250 horses at a given speed, or range of speed. torque is like a powerful, strong twisting force, like curtis said, using a wrench, because you use them slowly with lots of force. you cant use the same force if you're swingin a hammer, its just completely different force

you can swing a hammer with force, but its nothing like the force you use for tightening a bolt with a wrench, the reason why the peak torque is always at a lower RPM that the peak bhp (right ?) is because the engine generates the slower "twisting" force going slower that the "hammer-like" swinging/rotating force of the horsepower.

i hope thats clear
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Old 09-04-2005, 02:19 PM   #7
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Re: Re: What is the difference between HP and Torque

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Originally Posted by 2.2 Straight six
the reason why the peak torque is always at a lower RPM that the peak bhp (right ?) is because the engine generates the slower "twisting" force going slower that the "hammer-like" swinging/rotating force of the horsepower.
No.

The reason peak torque is always at a lower RPM than peak, HP is simply because Torque IS horsepower across time. I am not sure why this concept is so difficult to grasp.

You cannot simply say is torque or Hp better. One is a derivitive of the other.
Again. HP = (Torque x RPM) / 5252 (5252 converts the circular movement to time)

Based upon the above.. ALL engines produce the same torque and hp at 5252 RPM. This is simply a mathematical fact since Torque is HP across time.

EG. Two engines.. One produces 200 lbs of torque at 5252 RPM. At that point it is producing 200 HP.

Another produces 210 lbs of torque at 4800 RPM. At that point it is producing only 182 HP. However that same engine might produce 160 lbs of torque at 7500 RPM. At that point it is producing 228 HP.

Got it?

HP is WORK, Torque is force. (typically a circular force)

To convert this into something even simpler.

I have two laborers, pushing blocks of mass across the room. One can only push a 100 lb block and it takes him 20 seconds to move it 100 feet.
The other laborer can move a 200lb block but it takes him 45 seconds to move it 100 feet. The first laborer produces more HP (work). However the 2nd laborer produces more torque (force). In an hour, laborer number one will do more work. (HP)

Now for a selection of laborers.... IF I HAD to move 200 lb blocks. I would choose the 2nd laborer. He, at least can perform that work. If I simply had to move 100 lb blocks, I would choose the 2nd. He would be able to perform more work in a given time.

In the example above the second laborer is a Diesel, or big block low RPM engine. The first laborer is a small 18,000 RPM Indy car.

Given all the above, Torque/HP choice should be based upon the weight of the vehicle and what you plan to do with it. Gearing can be used to get the engines to comparable output torque, but gearing also has drawbacks.

There are lots more to this, but that is about as simple as I can make it.

Jim
SR Racing Inc.
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Old 09-04-2005, 07:47 PM   #8
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Re: What is the difference between HP and Torque

my head hurts...
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Old 09-04-2005, 10:54 PM   #9
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Re: What is the difference between HP and Torque

Well the way I've always understood this "abstract" concept is. TORQUE = WORK,TURNING FORCE, EFFORT. HORSE POWER is just a representation of the rate of speed that work is accomplished in! Example, I've got a 31Hp tracter that can outpull most 200HP cars because it produces lots of TORQUE! But its slow because the rate at which that torque is utilized is low (31Hp)! A engine is costantly produceing torque even when its not being utilized for motion. This force is modified by the drivetrain to achieve required perameters for driveability. Horsepower stripped to the bone is basicly if one horse can move a load this far in this amount of time, then 2,3,4, ETC horses can perform that same feat this much faster! But the loads the same! (You can wake up now!)
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Old 09-04-2005, 11:38 PM   #10
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Re: What is the difference between HP and Torque

HP is like skittles, its bright and shiny. M&M's are like Torque, because some of them have nuts.
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Old 09-05-2005, 11:42 AM   #11
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asemstr,

You got it right! (Except the horse to HP correlation. That was an estimate by Watt in the 18th century that turned out to be incorrect, but that was his best guess at the time.)

Jim
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Old 09-05-2005, 12:02 PM   #12
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Re: What is the difference between HP and Torque

Torque is like a girl you'd marry; pretty, gets things done, reliable.

Horsepower is like a prostitute; sounds like a good idea when you buy it, but there's nothing on the inside you really want to experience.

By the way; that was the analogy we used internally at GM
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Old 09-05-2005, 11:39 PM   #13
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Re: What is the difference between HP and Torque

And that explains why GM guys are screwwed up!
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Old 09-07-2005, 01:04 AM   #14
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Re: Re: What is the difference between HP and Torque

Quote:
Originally Posted by sracing
As simple as possible,.... HP is a unit of work. Torque is a unit of Force. The more force that can be applied over a given amount of time. the more work (HP). In a sense, Torque and HP are the same thing. However, if more torque can be applied over the same amount of time, more work (HP) can be done.




"Good" engine? Don't know. Depends upon what you want it to do. Engines can be designed to produce lots of different torque at many different RPM points. It depends upon what you want that engine to do and at what RPM.

Jim
SR Racing
GUYS THE DIFF. IS TORQUE IS JUST HOW MUCH HP THAT U PUT TO THE REAR TIRES AND TO THE PAVEMENT OR VICE VERSA. YOU NEVER WANT MORE HP THAN TORQUE
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Old 09-07-2005, 04:43 AM   #15
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Re: Re: Re: What is the difference between HP and Torque

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Originally Posted by TRACYCULBERSON
GUYS THE DIFF. IS TORQUE IS JUST HOW MUCH HP THAT U PUT TO THE REAR TIRES AND TO THE PAVEMENT OR VICE VERSA. YOU NEVER WANT MORE HP THAN TORQUE
Huh? I think you need to do some reading. You haven't quite grasped the concept.

Jim
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