what exactly is horsepower
Hello, I was asked a rather simple question today, but I found myself stumped. I am wondering if anybody could enlighten me with their knowledge. The question is: What exactly is horsepower (in terms of engines)? I looked the term up online, and it told me that 1 hp is equal to 550 ft-lbs per second. It also told me that James Watt compared the power of steam engines (back in the day) to that of horses. That doesn't tell me much, I also looked in the forums, and didn't find anything. Also, what is the definition of torque? Furthermore, what about rwhp? Thanks for your help.
Here you go http://www.g-speed.com/pbh/torque-and-hp.html
[ March 04, 2003: Message edited by: Mirror Image ]</p>
An old, old article from the 9th issue of The Hotrodder:
What is horsepower?
Think you already know? Think again.
Let's start with some brief history (if you thought I'd let
you get away without a minor automotive history lesson, this
is probably your first issue of The Hotrodder ;-) ).
Besides being a term that people throw around constantly
these days when talking about cars, it is actually a very
specific measurement defined about 200 years ago by James
James Watt was instrumental in vastly improving the quality
of the steam engine in the late 1700's (translation: he made
it so that it wasn't prone to blowing up all the time).
Although he coined the term "horsepower", he gained more
fame by having his last name associated with a common energy
measurement (think about that the next time you change a 40
"Watt" light bulb).
Anyway, good ol' James Watt was an engineer who worked on
steam engines. Back then, one of the first potential uses
for engines was not in cars, but in mines, where horses were
used to pull mined coal out of the deep mine shafts.
The horse's halter was attached to a rope which ran through
a pulley and stretched down vertically into the coal mine.
Watt wanted a way to specifically measure and quantify the
amount of work that one horse could do. He also wanted to
relate this figure to the amount of work that one of his
steam engines could do. That way, when he was trying to sell
an engine to someone, he could say that it had, for example
"15 horsepower" meaning that it could do the work of fifteen
He figured that a single horse could lift about 330 pounds
of coal 100 feet up the mine shaft in one minute. 330 pounds
times 100 feet equals 33,000 foot-pounds. When this was
completed in one minute, Watt determined it to be equal to 1
horsepower. So 1 horsepower is equal to a certain amount of
work (330 pounds lifted 100 feet) done in a certain amount
of time (1 minute) -- 33,000 foot-pounds per minute.
So now Watt had an easy way to let coal mine operators know
how much money and resources they could save by using his
new steam engine.
I like to think the conversation went a little something
JAMES WATT: "Good day to thee, Mr. Coal Mine Owner. I have a
device which shall significantly improveth the efficiency of
thy coal mine."
COAL MINE OWNER: "How can that be Mr. Watt? Have thee
invented a stronger horse?"
JAMES WATT: "Hardly, my good fellow. Rather, I have for thee
something that I calleth a steam engine."
COAL MINE OWNER: "Steeme enjin, my knickers! I have heard
that they are inefficient, and oft bloweth up!
JAMES WATT: "No longer, my good man. My steam engine is far
superior to thy horse. It runneth on coal, not horse feed,
and it doth not crappeth all over the place."
COAL MINE OWNER: "Thy engine sounds good, Mr. Watt. But how
much stronger is it than one good horse?"
JAMES WATT: "It doth replaceth 15 horses, my good man, for
it produceth 15 horsepower"
COAL MINE OWNER: "Horsepower, ye sayeth? And 15 horsepower
no less? That is quite remarkable, my good man. I shall
buyeth four score of thy steeme enjins."
JAMES WATT: "Thank ye kind sir. I accepteth payment in
silver, gold, or sheep. In fact, I improveth daily upon my
engine, and I expect that one day, mankind shall createth
an engine which shall produceth 300 horsepower, and thus
replace 300 horses."
COAL MINE OWNER: "Ye make a fine enjin, Mr. Watt, but, ye
are, as they sayeth, a few apples short of a bushel! 300
horsepower, my knickers!"
Well...something like that. Anyway, if I were James Watt, I
might have called it Wattpower, but maybe he had a hunch
that in 200 years, his name would be on every light bulb in
It's that simple. 1 horsepower equals 33,000 foot-pounds per
minute or...550 foot-pounds per second. So, a one horsepower
horse will move 330 pounds of weight 100 feet in one minute.
Same for a one horsepower engine (at 100% efficiency --
we know that's impossible, but you get the point).
So...to produce the same amount of power that a 300
horsepower engine does, you would have to hook up 300 horses
to your car. Good luck.
Horsepower also converts easily into other common units of
measurement. One horsepower is equal to 746 watts. So...an
engine running constantly and producing one horsepower could
run an electric generator which produced 746 watts. Hook
that generator up to an electric heater and it will produce
2,545 BTU's of heat in one hour (a BTU, or British Thermal
Unit, is the amount of energy needed to raise the
temperature of water one degree Fahrenheit).
If you want to sound like a real horsepower geek, you can
refer to a 60 watt light bulb as a 0.0804 horsepower light
The average person has about 0.1 horsepower (pathetic, I
know). So it would take about ten people to make up one
measly horsepower. That means you would need about three
thousand of your good friends hooked up to the front of your
car to equal a 300 horsepower engine.
Certainly not impossible, but highly unlikely. However, if
you do manage to tie up 3,000 of your good buddies to the
front of your car, we would love to see a picture of it.
Please send all pictures of 3,000 friends tied to the front
of your car to: email@example.com.
During the "horsepower wars" of the 1960's, car companies
were testing the horsepower of their engines without
necessary accessories such as alternators, and even without
water pumps, so that they could report higher horsepower
figures for the public. This devious plan backfired on the
car manufacturers when insurance companies began to charge
higher rates for higher horsepower vehicles. So, the car
manufacturers then began listing their cars at a
lower-than-actual horsepower rating.
Fortunately, this all came to an end in the early 1970's
when the SAE (Society of Automotive Engineers) stepped in to
standardize the testing procedures and provide everyone with
reliable horsepower figures.
Car manufacturers can still be pretty slick though, and
oftentimes, the engine that they are testing their
horsepower on is an expertly tuned version running in
controlled conditions in a laboratory, rather than a
production line engine as you might expect in your vehicle.
Why do engine horsepower ratings differ greatly from the
actual horsepower that your car puts under your foot? This
is a simple one, but we'll break it down.
There is a basic law of physics that states that in any
energy generating system (such as your engine) some of the
energy will be lost -- this is referred to as energy
dissipation. Energy (in this case horsepower) is always lost
due to friction, air resistance, or viscosity. Each time
that energy is transferred, it is exposed to more of the
forces that steal some of the energy.
Sorry folks, you just can't get around that one. Add to that
the fact that an engine has to transfer its power through a
transmission, through a rear differential, through a pair of
axle shafts, and then to your rear wheels, and you'll see
how you lose a good amount of that energy.
There is actually a metric horsepower rating, although
recent laws require you to be wearing a pocket protector and
extremely thick glasses to use it. One SAE horsepower
is equal to 1.0138697 metric horsepower. Pretty close.
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thanks, really appreciate it. I guess that that the horse pulling an amount of coal a certain amount of feet is the only way to look at it. Again, thanks a bunch. This is a bad *** website, and I look forward to looking for you guys advice soon. Thanks again.
Jon, I gotta give you the award for the best laugh I had all week. Thanx a million. You've got such great creativity it's no wonder this is the best dang site ever!!!! Love the Dialog.
Holy crappeth Jon, are your fingers bleeding after all the typing?
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