Can someone explain in laymans terms the difference between Horsepower and Torque?

Sluggo

Lifer
Jun 12, 2000
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I am trying to teach Mrs. Sluggo a little about cars, but I cant get her to grasp the difference between HP and Torque. I know in my mind what it is, but I cant seem to come up with an analogy that she can relate to.

Any ideas?
 

pen^2

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Apr 1, 2000
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from my limited knowledge i could tell you torque has to do with a vehicles tolling capacity and HP with acceleration... could be wrong :)
 

Buzzman151

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Apr 17, 2001
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Tell her that she's a woman and she can't get it. But.... only if you wanna sleep on the couch tonight. I wouldn't personally but just another option. :cool:
 

blueghost75

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Dec 12, 2000
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here is my understanding:

tourque and horsepower are a measure of the same thing, but in different units. Horsepower ratings are giving at the higher RPMs, and tourque ratings are given at the lower RPMs. is this correct?
 

blueghost75

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Dec 12, 2000
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let me re-phrase that a little. tourque is generally used to measure the amount of power the vehicle puts out at lower RPMs. horsepower is generally used to measure the amount of power the vehicle puts out at higher RPMs. again, please correct me if i am wrong
 

Colt45

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Apr 18, 2001
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torque is like the Haulin' ass kinda thing,
while HP is like overall potential power or somthing..
 

morkinva

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Nov 16, 1999
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I always thought that torque was the ability to spin the wheels. A car with a lot of low-end torque is difficult to get rolling on a slick road without spinning the wheels faster than necessary. It is harder to get a car with not so much low-end torque to 'light em up' on dry pavement (like a turbo, unless you release the brake while the rpm's are greater than 1000 -- also known as 'torquing it down')

I also have always been confused by these two. But according to the howstuffworks website, these two are related by an equation for a particular rpm so now I'm even more confused.
 

Sluggo

Lifer
Jun 12, 2000
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I have kind of explained it to her like the website that was mentioned here.

Torque, Power to turn things (wheels)

HP, Power to make things move (car goes fast)

She considers this explanation to be the exact same statement, only worded differently.

Watching Junkyard Wars where they made dragsters in America, and explained how taller or shorter back tires can effectively impact the final drive ratio helped out my explanation a bit for her, but she just isnt grasping the whole concept.

 

blueghost75

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Dec 12, 2000
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the problem is that tourque and horsepower ARE the same thing. they are both measures of the same thing, just in different applications.
 

morkinva

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To say that torque and horsepower are the same thing is absolutely wrong. You are not taking into account the particular rpm that is required for the conversion. The torque curve is different from engine to engine, like a pickup has the torque curve and gearing skewed towards the lower rpm's so as to pull a static load.

I just looked on deja.com and this stuck out:

Look at it this way: Torque is an instantaneous measure of the
pressure generated in the cylinder during combustion; if you average
torque over a crankshaft revolution, then multiply times rpm, you get
horsepower


or this:

To put it in the simplest terms. Torque is responsible for the rate of
acceleration. The more torque the faster the acceleration. Torque is a
measurement of twisting force. Horsepower relates to speed rather than
acceleration. The more horsepower, the higher the speed. HP is directly
responsible for (top) speed (removing aerodynamic considerations).

Torque equates to acceleration
Horsepower equates to speed



If you change the diameter of the drive wheel(s) you change the torque curve (as mentioned in a previous post). So torque is a function of horsepower at a given rpm, but its curve can be changed by things like gearing, drive wheel size, etc.
 

TuffGuy

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Jul 6, 2000
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torque and power are not the same thing, but they are a little related. power can be achieved at high RPMs without a lot of torque, like you get with imports. torque is more "break-neck", and is generally a lot more dependent on displacement. (i think)
 

Burn

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Oct 9, 1999
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Think of it this way: torque is how heavy an object you can lift, while horsepower is how fast a given object can be lifted.
 

blueghost75

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Dec 12, 2000
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lemme rephrase this again: tourque is the amount of power at lower RPMs, and horsepower is the amount of power at higher RPMs. I think it would be accurate to say that tourque and horsepower are the measure of the same thing.

This one quote stuck out to me: So torque is a function of horsepower at a given rpm

I think that best describes the difference/relation of torque and horsepower.
 

Burn

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Oct 9, 1999
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<< lemme rephrase this again: tourque is the amount of power at lower RPMs, and horsepower is the amount of power at higher RPMs. >>



Sorry, you are a little misguided.
 

RossGr

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Jan 11, 2000
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<< << lemme rephrase this again: tourque is the amount of power at lower RPMs, and horsepower is the amount of power at higher RPMs. >> >>



Actually way misguided

To compare torque and horsepower all you need to do is look at the fundamental units, it is clear then that they are not the same thing.

Torque = ft-lb

Horsepower = ft-lb/sec

So 100 ft-lbs of torque can be generated by applying 100lbs at a distance of 1ft (imagin a long wrench) or by 50lbs on a 2ft wrench.

Horsepower is the rate at which the torque can be produced. As indicated in the above links you must multibly torque by the engine speed to get the horsepower (there is a conversion factor also).
 

Sluggo

Lifer
Jun 12, 2000
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<< To put it in the simplest terms. Torque is responsible for the rate of
acceleration. The more torque the faster the acceleration. Torque is a
measurement of twisting force. Horsepower relates to speed rather than
acceleration. The more horsepower, the higher the speed. HP is directly
responsible for (top) speed (removing aerodynamic considerations).
>>



That is basically how I was taught it. With the exception that Torque not HP is the limiting factor in Top Speed.

At such speed where the wind resistance overcomes the motors ability to turn the drive wheels with any greater force.
 

pen^2

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Apr 1, 2000
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i knew what physics definition of torque vs Hp is, but could you put it in real world performance terms? waht does torque exactly do on cars?
 

Jamestl

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Sep 10, 2000
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Tq is a measurement of force at any given instant. HP takes into account engine speed.

here's the equation for calculating HP: (torque x RPM) / 5252 (i think).

so let's suppose you have a flat torque curve from idle to 8000 RPM redline, your acceleration would stay the same (if we ignore wind resistance), but the engine would produce the most power at 8000RPM.
 

PullMyFinger

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Mar 7, 2001
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STOP THE PRESSES!
Sorry, just felt like saying that. Let me try to clarify this (I'm an engineer and I'm here to help). Torque is force, force times distance is work, power is work per unit time. Therefore, horsepower is derived from torque. A dynomometer measures the amount of torque an engine can produce at each specific rpm. The equation provided by Jamestl is then used to determine the horsepower at each specific rpm.

This is possibly the best example I can think of to describe the difference between torque and horsepower. Suppose you have a heavy weight on the ground which will be lifted vertically with a hand-cranked winch. In order to just barely lift the weight, you must apply 10 lb of force on the winch handle, this creates torque (force X distance about a stationary point). Now, lets suppose you need to lift the weight 10 feet. This will require you to apply the 10 lb of force to the handle for a set number of turns, thus creating work. Now lets assume that you want to lift the weight to 10 feet in 10 seconds. This will require X amount of power. Now suppose you want to lift the same weight up to 10 feet in only 5 seconds. You will now have to apply the same 10 lb of force to the handle but now you will have to spin the handle twice as fast. This will require twice the power as the original lift.

An electric engine has a flat torque curve, ie it produces the same amount of torque at any rpm. An internal combustion engine is slightly different because of intake and exhaust variables and produces a torque curve with peaks and valleys throughout the rpm range of the engine. A forced induction (turbo, supercharged) engine has qualities of both. It's torque curve resembles a normally aspirated engine until the point when boost is created. From that point until the flow limit of the cylinder head is reached, the torque curve will be essentially flat.

Horsepower and torque can be difficult to understand and/or explain so if all else fails try this. Tell her that torque is what happens when you first hit the gas and horsepower is what happens when you leave your foot to the floor for a while.

Hope this helps to clarify things.