simple definition of torque "vs" horse power

[Jerome P.]

Simply put; torque is the amount of work being done and horse power is how quickly the work is done?

Am I wrong? If so what is a quick and easy definition of torque and horse power?

[Kurt G.]

Re: simple definition of torque "vs" horse power

Per Websters New World Collegiate, torque is the measure of the tendency of a forece to cause rotation, equal to the force multriplied by the perpendicualr distance between the lin of action of the force and the produce rotation. Horsepower is a basic unit of power in the feet per second system, equal to the power needed to raise a weight of 550 lbs a distance of 1 foot in 1 second, or 746 watts, or 42.41 BTU

Now, simply, torque is the resistance to twisting, as horsepower is the ability to move. In basic terms the more horsepower available, the more torque produced, in simple applications. There are however several factors, in an internal combustion engine that affect the HP/torque ratio. One big one is compression ratio. An engine with 11.0:1 compression ratio will move more (produce more torque) than an engine with 8.5:1 compression. Look at the numbers between the '71 350 small block and the '72 350 small block. Lower compression, lower torque. More resistance to movement (all accessories attached to the engine used in rating) less horsepower.

Not simple, it's physics.

[Jim R.]

Re: simple definition of torque "vs" horse power

My Definition is (Torque wins races Horsepower sell's cars)

[Duke W.]

Re: simple definition of torque "vs" horse power

Torque is a force applied in a circular rather than linear direction.

Power is energy per unit time which is force applied over a distance in a period of time, and the faster you apply energy to a vehicle, the faster it accelerates. Thus, it's power, not torque that accelerates a car.

A large displacement engine produces high torque because torque is a primarily a function of displacement and compression ratio, but volumetric efficiency enters into the equation, which is why engines don't have flat torquer curves. High torque at low revs means high horsepower at low revs, which is why large displacement engines are very satisfying in normal driving. You don't have to wait for engine revs to build to feel he car accelerate strongly. High torque at low revs means high horsepower at low revs.

Say an engine produces 250 lb-ft of torque at 6000 revs, which can be characterized as a 250 pound force acting in a circular motion at a radius of one foot. The amount of energy it produces in one minute is the distance that force is applied, which is 2pi radians times the radius of one foot - the length of a full circle arc - times 6000,so we have a force acting over a given distance in a given time, which is power:

250 x 6.28 x 6000 = 9,420,000 lb-ft/sec

In the late eighteenth century James Watt needed a way to size his new steam engine to replace the horse powered water pumps in English coal mines that prevented them from flooding. His time and motion studies led him to define "one horsepower" as 33,000 lb-ft per minute or 550 ft-lb/sec- which is the continuous output an average draft horse could develop for a couple of hours. He thus develped one, two, three, four... "horsepower" steam engines to replace horses to drive the pumps.

So the above nine million plus ft-lb/sec of energy per unit time is equal to about 285 horspower. If that same engine produces 250 lb-ft at 1500 revs it's making about 71 HP at that speed.

If you do the proper unit conversions to express torque in pound-feet and engine speed in revs/minute you come up with the familiar formula:

Horespower = torque in lb-ft x RPM/5252

Duke

[Bill M.]

Re: simple definition of torque "vs" horse power

Simply put; torque is the amount of work being done and horse power is how quickly the work is done?

Am I wrong? If so what is a quick and easy definition of torque and horse power?

torque: force at a distance (no motion required)

energy: force through a distance (motion required)

horsepower: energy per unit time

units of torque: lb-ft

units of energy: ft-lb

horsepower is ft-lb/sec, not lb-ft/sec

This is a lot clearer in the metric system...

[Philip A.]

Re: simple definition of torque "vs" horse power

In the setting of cars and simplicity, I was taught torque = acceleration and horsepower = top speed (potential). So ALL else being equal (which it never is; and this is all dynamic per the dyno): 1) the car with higher torque accelerates more rapidly (0-60 time) to its top speed; and 2) the car with the higher HP, accelerates less rapidly (0-60 time) to a higher top speed.

[Duke W.]

Re: simple definition of torque "vs" horse power

Not true. Simplication can loose the essence of the physics. Torque is a static measurement. Power is a dynamic value.

The car with the greatest average applied horsepower through a given distance will get there faster with a higher top speed. Torque is half the equation, RPM is the other half, so gearing has to be taken into account.

That's why a short geared SHP small block can be both quicker (et) and faster (trap speed) than a tall geared L-36 in the quarter mile even though the L-36 has greater peak torque and power.

Duke

[Jack M.]

Re: simple definition of torque "vs" horse power

The simple 'seat of the pants' definition I learned long ago:
You drive torque...not horsepower.

[Duke W.]

Re: simple definition of torque "vs" horse power

That's true for road engines, especially modern ones that make 80-90 percent of peak torque at 1500. You don't need to rev them very high in normal driving.

It's not true for 15,000 rev motorcycles or 18,000 rev F1 engines that won't get out of their own way below 5-6000.

That's why I emphasize low end torque - no less than 80 percent at 2000 for SHP engines with manual transmissions and 90 percent at 2000 for autos - in my road engine configurations and plead with people to start dyno tests at 1000-1500 revs, not the usual 3000-3500 that most dyno operators use, but I loose most of those battles. Nobody listens.

Duke

[Terry D.]

Re: simple definition of torque "vs" horse power

Someone just read their new copy of Chevy High Performance magazine

[Monte M.]

Re: simple definition of torque "vs" horse power

I know this is not exactly true, but I explained it the easiest way I could to my son by saying:

Torque = The initial pulling power or force that gets you going.

Horsepower = The force that keeps you going once the initial thrust of the torque is gone. It is more stable.

I know this does not break down like this exactly, but it got the basic idea across to my son. Horsepower to me was always "the work being done" and Torque was "getting the work started"
Hope it helps, and I am open for any additional input.

It takes a lot of torque to get me out of bed in the morning (ha ha)

[Jerome P.]

Re: simple definition of torque "vs" horse power

Thanks to everyone. Your thoughts and input are appreciated.