MichaelTT

and what is interesting it is all very correct from a physics standpoint...and that is an excellent starting point in understanding automotive engineering...so here is the post...
Force, Work and Time
If you have a one pound weight bolted to the floor, and try to lift it with one pound of force (or 10, or 50 pounds), you will have
applied force and exerted energy, but no work will have been done. If you unbolt the weight, and apply a force sufficient to lift the
weight one foot, then one foot pound of work will have been done. If that event takes a minute to accomplish, then you will be
doing work at the rate of one foot pound per minute. If it takes one second to accomplish the task, then work will be done at the
rate of 60 foot pounds per minute, and so on.

In order to apply these measurements to cars and their performance you need to address the three variables of force, work and
time.

Awhile back, a gentleman by the name of Watt made some observations, and concluded that the average horse of the time
could lift a 550 pound weight one foot in one second, thereby performing work at the rate of 550 foot pounds per second, or
33,000 foot pounds per minute, for an eight hour shift, more or less. He then published those observations, and stated that
33,000 foot pounds per minute of work was equivalent to the power of one horse, or, one horsepower.

For purposes of this discussion, we need to measure units of force from rotating objects such as crankshafts, so we'll use
terms which define a *twisting* force, such as foot pounds of torque. A foot pound of torque is the twisting force necessary to
support a one pound weight on a weightless horizontal bar, one foot from the fulcrum.

Now, it's important to understand that nobody on the planet ever actually measures horsepower from a running engine. What
we actually measure (on a dynamometer) is torque, expressed in foot pounds, and then we *calculate* actual horsepower by
converting the twisting force of torque into the work units of horsepower.

Visualize that one pound weight we mentioned, one foot from the fulcrum on its weightless bar. If we rotate that weight for one
full revolution against a one pound resistance, we have moved it a total of 6.2832 feet (Pi * a two foot circle), and, incidentally,
we have done 6.2832 foot pounds of work.

OK. Remember Watt? He said that 33,000 foot pounds of work per minute was equivalent to one horsepower. If we divide the
6.2832 foot pounds of work we've done per revolution of that weight into 33,000 foot pounds, we come up with the fact that one
foot pound of torque at 5252 rpm is equal to 33,000 foot pounds per minute of work, and is the equivalent of one horsepower. If
we only move that weight at the rate of 2626 rpm, it's the equivalent of 1/2 horsepower (16,500 foot pounds per minute), and so
on. Therefore, the following formula applies for calculating horsepower from a torque measurement:

Torque * RPM
Horsepower = ------------
5252


The Case For Torque

Now, what does all this mean in carland?

First of all, from a driver's perspective, torque, to use the vernacular, RULES :-). Any given car, in any given gear, will accelerate
at a rate that *exactly* matches its torque curve (allowing for increased air and rolling resistance as speeds climb). Another way
of saying this is that a car will accelerate hardest at its torque peak in any given gear, and will not accelerate as hard below that
peak, or above it. Torque is the only thing that a driver feels, and horsepower is just sort of an esoteric measurement in that
context. 300 foot pounds of torque will accelerate you just as hard at 2000 rpm as it would if you were making that torque at
4000 rpm in the same gear, yet, per the formula, the horsepower would be *double* at 4000 rpm. Therefore, horsepower isn't
particularly meaningful from a driver's perspective, and the two numbers only get friendly at 5252 rpm, where horsepower and
torque always come out the same.

In contrast to a torque curve (and the matching pushback into your seat), horsepower rises rapidly with rpm, especially when
torque values are also climbing. Horsepower will continue to climb, however, until well past the torque peak, and will continue
to rise as engine speed climbs, until the torque curve really begins to plummet, faster than engine rpm is rising. However, as I
said, horsepower has nothing to do with what a driver *feels*.

You don't believe all this?

Fine. Take your non turbo car (turbo lag muddles the results) to its torque peak in first gear, and punch it. Notice the belt in the
back? Now take it to the power peak, and punch it. Notice that the belt in the back is a bit weaker? Fine. Can we go on, now? :-)

The Case For Horsepower

OK. If torque is so all-fired important, why do we care about horsepower?

Because (to quote a friend), "It is better to make torque at high rpm than at low rpm, because you can take advantage of
*gearing*.

For an extreme example of this, I'll leave carland for a moment, and describe a waterwheel I got to watch awhile ago. This was
a pretty massive wheel (built a couple of hundred years ago), rotating lazily on a shaft which was connected to the works inside
a flour mill. Working some things out from what the people in the mill said, I was able to determine that the wheel typically
generated about 2600(!) foot pounds of torque. I had clocked its speed, and determined that it was rotating at about 12 rpm. If
we hooked that wheel to, say, the drive wheels of a car, that car would go from zero to twelve rpm in a flash, and the waterwheel
would hardly notice :-).

On the other hand, twelve rpm of the drive wheels is around one mph for the average car, and, in order to go faster, we'd need
to gear it up. To get to 60 mph would require gearing the wheel up enough so that it would be effectively making a little over 43
foot pounds of torque at the output, which is not only a relatively small amount, it's less than what the average car would need
in order to actually get to 60. Applying the conversion formula gives us the facts on this. Twelve times twenty six hundred, over
five thousand two hundred fifty two gives us:

6 HP.

Oops. Now we see the rest of the story. While it's clearly true that the water wheel can exert a *bunch* of force, its *power*
(ability to do work over time) is severely limited.

Auto Union Jack

Someone e-mail ultimate lurker. Torque wins races, HP sells motors.

PanTTher

of course totally discounting the human factor side of it.

Auto Union Jack

Just say no to V TECH.