what is HP and torque

[en3d]

I have a general understanding of these measurements but what is the meaning of these measurements?

If you think of other measurements, like distance or weight there is a definitive quantity that you can relate to... so what is a horsepower and a torque?

[quickdraw]

If you go to: http://www.howstuffworks.com/horsepower.htm That will give you a good explaination of horsepower. Not sure on the torque though.

Tim

[Austin]

The best way I can describe it -

Torque is the ability of the engine to change speed under a given load.

Horsepower is the ability of the engine to maintain speed under changing load.


These are from dictionary.com... not much help:

torque1 (tôrk) n.
1. The moment of a force; the measure of a force's tendency to produce torsion and rotation about an axis, equal to the vector product of the radius vector from the axis of rotation to the point of application of the force and the force vector.
2. A turning or twisting force.

horse·pow·er (hôrspour) n. pl. horse·power
1. Abbr. hp A unit of power in the U.S. Customary System, equal to 745.7 watts or 33,000 foot-pounds per minute.
2. The power exerted by a horse in pulling.
3. Informal. Effective strength: political horsepower; computer horsepower.

horse power \Horse" pow`er\

1. The power which a horse exerts.

2. (Mach.) A unit of power, used in stating the power required to drive machinery, and in estimating the capabilities of animals or steam engines and other prime movers for doing work. It is the power required for the performance of work at the rate of 33,000 English units of work per minute; hence, it is the power that must be exerted in lifting 33,000 pounds at the rate of one foot per minute, or 550 pounds at the rate of one foot per second, or 55 pounds at the rate of ten feet per second, etc.

Note: The power of a draught horse, of average strength, working eight hours per day, is about four fifths of a standard horse power.

Brake horse power, the net effective power of a prime mover, as a steam engine, water wheel, etc., in horse powers, as shown by a friction brake. See Friction brake, under Friction.

Indicated horse power, the power exerted in the cylinder of an engine, stated in horse powers, estimated from the diameter and speed of the piston, and the mean effective pressure upon it as shown by an indicator. See Indicator.

Nominal horse power (Steam Engine), a term still sometimes used in England to express certain proportions of cylinder, but having no value as a standard of measurement.

3. A machine worked by a horse, for driving other machinery; a horse motor.

[Austin]

Oh, and for torque:

http://www.howstuffworks.com/torque.htm

[nhluhr]

Originally posted by Austin
The best way I can describe it -

Torque is the ability of the engine to change speed under a given load.

Horsepower is the ability of the engine to maintain speed under changing load.

eh... that's a little meaningless since the way you describe them have nothing to do with what they really are.

Layman's terms:

As you recall from high school physics, an object in motion tends to stay in motion, an object at rest tends to stay at rest, until a force acts upon it. In cars, you have the engine exerting force (torque) to accelerate it but you also have wind resistance, drivetrain drag, friction from the tires, etc exerting a force to slow it. Your engine is CONSTANTLY exerting its torque force to keep the car from decelerating.

Torque is the REAL meaningful measurement you need to look at if you want to FEEL your car accelerate.

Now, you might also recall that power the rate at which energy is being applied to a system. It just so happens that in a car,

hp = torque*rpm/5252

Horsepower and torque will always be related but while it may look from a hp curve that your car is making almost no power at low rpms, this certainly doesn't mean your car isn't accelerating as fast or faster than it would be at high rpms, since it is entirely possible to make high torque at low revs, and as stated above, torque is the force that accelerates.

However, since we have gearing in cars, it is useful to quote hp numbers since certain cars are able to rev much higher than others. Take the Honda S2000, for example with a redline of 9000. This car ONLY has 153lb-ft of torque at the flywheel and honestly does NOT feel very fast when you floor the gas pedal. It is merely able to accelerate at easier-to-push gear ratios for much longer than the 7000rpm redline WRX. The easier gear means more force is put to the tire which is what ultimately pushes the car down the road.

If the same two cars were to never go over the WRX's redline, it would be PHYSICALLY IMPOSSIBLE for the S2000 to be a faster car since it has a much higher amount of torque being put to the wheels by the engine.

For even more info, read that www.howstuffworks.com page thoroughly. There are lots of related links on it too which are wonderfully informative.

[Jeff 2.5RS]

This website has been useful for me.