It can be deceiving.


http://en.wikipedia.org/wiki/Horsepower

Horsepower
From Wikipedia, the free encyclopedia.

The horsepower (hp) is the name of several non-metric units of power. In scientific discourse the horsepower is rarely used due to the various definitions and the existence of an SI unit for power, the watt (W). However, the idea of horsepower persists as a legacy term in many languages, particularly in the automotive industry for listing the maximum power of internal-combustion engines.

The various types of horsepower are:
Contents


* 1 Horsepower (hp)
* 2 Engine horsepower
o 2.1 Indicated horsepower (ihp)
o 2.2 Brake horsepower (bhp)
+ 2.2.1 hp (SAE)
o 2.3 Drawbar horsepower (dbhp)
o 2.4 Shaft horsepower (shp)
o 2.5 Effective horsepower (ehp)
o 2.6 Summary for a ship
* 3 RAC horsepower
* 4 Metric horsepower
o 4.1 PS
o 4.2 pk
o 4.3 CV
o 4.4 ch
* 5 Boiler horsepower
* 6 Electrical horsepower

Deceiving or not, encyclopedias aside, my point remains. Torque is not a measure of acceleration, power is.

BTW, most of modern measurements are in brake horsepower.



That's all well and good. If you're going to write a scholarly discourse on the application of certain types of power in certain types of situations, you can use watts if you want. All that statement is saying is that a "horsepower" is a strange unit (746 watts if I remember correctly, something like that). Sure, its a convention that we use it when referring to cars. If you'd like to refer to your measurements of power in units of watts in the future, you can certainly do that, but I think you'll confuse some of our readers. The statement isn't saying that "power" is rarely used in scientific discussion, its saying merely that when they do talk about power, they usually use another unit. In paralell, scholarly discussions of distance and length are generally done in the metric system. Sure, you can convert those units to english measurements like feet and inches if you want, it just happens that metric units are easy to deal with.

Folks still measure the height of horses in "hands" too. Its a strange unit, and outside the realm of horses, somewhat nonsensical. All that means, though, is that you have to do a unit conversion if you want to know what that means in another unit, such as meters or feet.

K

Well, too answer the question, yes they did change it but not to make them more appealing as they now measure with all the accesories on. Some even measure at the output shaft of the transmission. There are several "Hp's" and like horses, they differ in strength from one to another.

A reading/measurement that doesn't change is Tq. it is measured at 1 pounds pull/twist thru the leverage of one foot, but can also be taken at different areas of a vehicle.

Remember as an engine spins faster it can be gear reduced in rpm to increase Tq...and this is where Hp comes into play. It allows you to know if, at a certain rpm, a gear reduction can produce an increase in Tq.

In the engineering discipline horsepower has a very precise and unambiguous definition. It is a unit of power in the US system of units (screwy as that is!) defined as 745.7 watts or 33,000ft-lb/minute. That unit can be converted to SI or any other form of power with the appropriate conversion factor. You would be just as correct to say "My engine puts out 26,0995 watts", or "Wanna see my 11,550,000ft-lb/minute monster", as to say "My engine puts out 350HP".

Past that proper usage, there are 101 different profane uses of the word that we all carelessly throw around, many of which are listed above. We all know what we mean. Most engineering terms are misused in casual conversation like "weight", "force", "mass", "energy", "velocity", "acceleration",etc.

Dang, y'all had me confuzzled with all the drawn out discourse on formulas and shtuff.

Torque does the work.

Horsepower is how quickly the work gets done.

Ya see, All that get's a bit muddled when you factor in mechanical multiplication, like gears and converters. That's why two identical vehicles, one with a bunch of high rpm horsepower and one with a boatload of low rpm torque could, theoretically, post identical E.T.'s and speeds with the correct gears and converter for each engine.

It ain't worth arguing about it though, it's been proven over and over since the beginning of drag racing.

Larry

I agree, TQ and HP are equal at 5,252 RPM. ALWAYS equal, NO exceptions. If TQ is a measurement of work and HP is a "measurement" of work over time then HP must be a derivative of TQ and RPM, it is NOT a seperate commodity.

I've seen many a high HP high winding small motor get caught and passed on the big end by a relatively low HP, "slow" revving TQ motor over the years. It's all in the total combination......