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Old 03-13-2005, 05:08 AM   #1
mumin
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HP vs Torque

I know this is one of those questions that I can search online but I think I learn better when someone tellsm me stuff:P I wanted to know what is they difference between horse power and torque. What if there is more torque than horse power..if possible..and other way?
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Old 03-13-2005, 05:17 AM   #2
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Quote:
Originally Posted by mumin
I know this is one of those questions that I can search online but I think I learn better when someone tellsm me stuff:P I wanted to know what is they difference between horse power and torque. What if there is more torque than horse power..if possible..and other way?
horsepower is used for top speed, torque is acceleration. so for 0-60 torque is better, and for lets say for a 1 mile staight track race H/P is better.
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Old 03-13-2005, 06:04 AM   #3
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Diesel engines usually have more torque than horsepower.

Torque is a turning force. Imagine yourself turning a wrench.

Horsepower is a measurement of work in a given time. Specifically 33,000 foot pounds per minute is equal to one horsepower.

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Old 03-13-2005, 06:59 AM   #4
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Quote:
Originally Posted by Import-tuner
horsepower is used for top speed, torque is acceleration. so for 0-60 torque is better, and for lets say for a 1 mile staight track race H/P is better.

Actually torque isn't for accelleration like you make it sound. If that was the case diesel engines would be owning all us gas guys, think about it.

Torque is turning force. The strength the motor is turning at, so it's relavent to how much you're going to be able to tow, or, how easy it is to maintain a speed, think of it that way.

Horsepower is relavent to accel/speed, the more horsies, the faster you're going to get from point A to point B. Think drag racing, you want a crazy amout of horse to get that beast to the other side of the track ASAP

It's actually a hard concept to explain, but once you understand it, it's really quite simple.
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Old 03-13-2005, 07:03 AM   #5
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Oh ok I get it.. There are upgrades that can give you horse power like better exhaust or air intake ...etc... are there upgrades to get more torque??
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Old 03-13-2005, 07:05 AM   #6
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Originally Posted by mumin
Oh ok I get it.. There are upgrades that can give you horse power like better exhaust or air intake ...etc... are there upgrades to get more torque??

Stroker kits are pretty much the only ones aimed at torque. But really, you improve one, the other goes up as well.
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Old 03-13-2005, 08:07 AM   #7
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Torque is just a force in a twisting motion. Take for example a wrench or a bicycle pedal. You power the wrench and in turn it twists and gives off torque, you pedal the bicycle and you twist the wheels and go foreward.

Horsepower is just power. The more horsepower you haev the faster and more efficiently you'll go.

You can't have 1000 torque and only 100 HP. YOu have to have an even amount of both.
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Old 03-16-2005, 11:11 PM   #8
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Quote:
Originally Posted by mumin
I know this is one of those questions that I can search online but I think I learn better when someone tellsm me stuff:P I wanted to know what is they difference between horse power and torque. What if there is more torque than horse power..if possible..and other way?

Forget all the tripe. Fuel is rated in joules and the when burnt at a rate of one joule per second releases a watt of power. How that power is applied whether it be for cooking steaks or to make a wheel turn is a product of that power.

Without power torque cannot exist, but power can exist without torque.

You cannot have more or less torque than power simply because they are different measurement, like oranges and lemons although they may share common elements. Just because someone decided to scale a graph to conveniently correlate with a 5252 derived constant does not mean one is greater than the other. The Torque (ft-lbs) = HP x 5252/rpm equation can be rearranged whichever way you like. If you use the same nonsense internet mechanics do by rearranging the the equation to prove hp is dependent on torque, you could equally argue power is dependent on rpm, which we all know is not true.

A convenient way for power to be measured is via a chassis dynamometer. One of the methods of measuring on the chassis dyno is tractive effort. From this you can apply gear ratios and wheel diameter data and find either a torque figure or a power figure or both at your leasure. Some people find it easier to find torque and then from that find power, but that is only stepping the maths.

For the relationship between acceleration and torque = simple school physics "torque and angular acceleration".
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Old 03-16-2005, 11:26 PM   #9
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Originally Posted by Wally
Forget all the tripe. Fuel is rated in joules and the when burnt at a rate of one joule per second releases a watt of power. How that power is applied whether it be for cooking steaks or to make a wheel turn is a product of that power.

Without power torque cannot exist, but power can exist without torque.

You cannot have more or less torque than power simply because they are different measurement, like oranges and lemons although they may share common elements. Just because someone decided to scale a graph to conveniently correlate with a 5252 derived constant does not mean one is greater than the other. The Torque (ft-lbs) = HP x 5252/rpm equation can be rearranged whichever way you like. If you use the same nonsense internet mechanics do by rearranging the the equation to prove hp is dependent on torque, you could equally argue power is dependent on rpm, which we all know is not true.

Just like in any math, you can rearrange the equation many ways. But that isnt' what we are talking about here and you should know it.

Torque is tangential force * the distance from the fulcrum. Power is defined as work per unit of time.

Applying 1 lb of force 1 ft from the fulcrum for a complete revolution will lead to;

W = F*2*pi*r = 1 lb * 2*pi * 1 ft = 2*pi lb-ft = 6.283 lb-ft

If it takes one minute to complete this revolution, then the power is;

P = W / time = 6.283 lb-ft / min

1 hp is defined as 550 lb-ft / s = 33,000 lb-ft / min

Therefore, applying 1 lb-ft of torque in one minute (1 rpm) = [6.283 lb-ft / min] / [33,000 lb-ft / min] = 1 / 5252 of 1 hp.

From this you can then calculate the number of hp from any given torque and rpm:

hp = torque (lb-ft) * rpm / 5252

No one "scaled a graph conveniently" to make that happen.

Where does the equation HP=TORQUE * RPM / 5252 come from? We will use Watts observation of one horsepower as 150 pounds, 220 feet in one minute. First we need express 150 pounds of force as foot pounds torque.

Pretend the force of 150 pounds is "applied" tangentially to a one foot radius circle. This would be 150 foot pounds torque.

Next we need to express 220 feet in one minute as RPM.

The circumference of a one foot radius circle is 6.283186 feet. ft. (Pi x diameter 3.141593 * 2 feet)

The distance of 220 feet, divided by 6.283185 feet, gives us a RPM of 35.014.
We are then talking about 150 pounds of force (150 foot pounds torque), 35 RPM, and one horsepower.

Constant (X) = 150 ft.lbs. * 35.014 RPM / 1hp

35.014 * 150 / 1 = 5252.1

5252 is the constant.

So then hp = torque * RPM / 5252



"The word horsepower was introduced by James Watt, the inventor of the steam engine in about 1775. Watt learned that "a strong horse could lift 150 pounds a height of 220 feet in 1 minute." One horsepower is also commonly expressed as 550 pounds one foot in one second or 33,000 pounds one foot in one minute. These are just different ways of saying the same thing. Notice these definitions includes force (pounds), distance (feet), and time, (minute, second). A horse could hold weight in a static position but this would not be considered horsepower, it would be similar to what we call torque. Adding time and distance to a static force (or to torque) results in horsepower. RPM, revolutions (distance) per minute (time), is today's equivalent of time and distance. Back to horses, imagine a horse raising coal out of a coal mine. A horse exerting one horsepower could raise 550 pounds of coal one foot every second."

Of course, the problem, as someone else pointed out in another thread, is that "Watt was simply observing that the horse lifted the 150 lb. object by 220 feet in one minute. We can't change that. Had Watt simply observed a bigger (say, a Clydesdale) or smaller horse (like Ford used to measure the '99 Cobra!) the definition of HP would be different."

The reason we dont measure internal combustion engine horsepower directly is that engies make a rotary motion, not linear motion. And unless the engine is geared down, the speed at which they do work (time and distance or RPM) is too great for practical direct measurement of horsepower. It seems logical then that the solution was to directly measure torque (rotational force eventually expressed in pounds at one foot radius) and RPM (time and distance, i.e. distance in circumference at the one foot radius) and from these calculate horsepower. Torque and RPM are easily measured directly.

Therefore when discussing internal combustion engines, torque IS the measured force, and hp is ALWAYS the calculated amount.
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Old 03-17-2005, 12:00 AM   #10
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I agree that measuring, for instance, tractive effort is convenient, but newtons is not newton metres nor is it watts. There is no need to even think about torque when deriving power from newtons over time.

I'll demonstrate the graphing in a diffrent way. Here is a nissan sss, from Newcastle Oz, dyno readout conveniently in british units. Where is the crossover at 5252?:



I guess you were trying to convey is the relationship of torque/hp by this:

hp = torque * RPM / 5252

@ 5252 rpm hp = torque
as rpm increases and power is static then torque decreases or if torque is to remain static the power input must increase?
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Old 03-17-2005, 03:10 PM   #11
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Wally

Your graph shows two different measurements of energy, and no measurement of torque. From Hobo's link: "Note that the SI units of torque is a Newton-metre, which is also a way of expressing a Joule (the unit for energy). However, torque is not energy."

Your graph thus doesn't display torque, merely two different units of energy. That's why the curves are very similar in shape and don't cross over.
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Old 03-17-2005, 10:48 PM   #12
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OK let me put it yet another way:

The simplified imperial formula is hp = ftlbs-force * RPM / 5252

when the rpms hit 5252 the result is power = torque *1

Now lets take the metric equivalent kW = N-m *RPM/ 9551

when the rpms hit 9551 the result is power = torque *1

In both instances we are dealing with the same effects, but with different units of measurements. As you can easily conclude if we used the same convention for graphing that is used for imperial power/torque curves the metric torque curve would not intersect the power curve until 9551 rpm.

As most daily grind engines run out of puff well before 9551 rpm we would not expect to see any intersection on our graph if it's x axis ceased @ 6500 rpm.


In so far as the shape of the tractive effort curve, do you really think it's shape will change by multiplying it by a constant rolling tyre radius and dividing by a constant drivetrain ratio? I don't think so somehow, so the curves are indeed valid and the bottom one is in fact the torque profile with a different scale.
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