"One hundred horsepower!"
Joe Clark whistled to himself as he read the specifications of one of the
new cars.
Gus Wilson, veteran auto
mechanic and Joe's partner in the operation of the Model Garage, merely
grunted. His mouth was too full of ham sandwich for articulate
expression.
"One hundred horsepower!"
Joe repeated. "That's a whale of a lot of power to be controlled by a
dinky little pedal under the toe of your
shoe. It's equal to fifty pairs of horses. Think of an auto able to
pull as strong as that many horses!"
"Why think of it when it
isn't so?" Gus growled as he fished a vacuum bottle from his lunch kit.
"Fifty pairs of horses could drag any auto ever made all over the lot."
"But I thought you told me
gasoline engine horsepower was the same as real horsepower," Joe protested.
"I did," admitted Gus.
"A one-horse-power gasoline motor, if you applied its power just right,
could lift 33,000 pounds one foot every minute all day long. It'd take
a pretty husky 'oat motor' to equal that."
"Then," Joe mused,
instinctively reaching for a pencil, "a hundred-horse-power motor ought to
be able to pull 3,300.000 pounds. Gosh! That's more pull than a
big politician has."
"That's right," Gus smiled.
"Figures don't lie, but sometimes they don't mean anything, either.
You could get that much pull out of a one-horsepower motor just as easy if
you geared it right. Trouble with you and a lot of other folks is you
don't know what horsepower really means."
"You said a one-horse engine
could lift 33,000 pounds," Joe argued. "If that's the bunk, then just
what is a horsepower anyway?"
"You forgot I said it could
lift that much weight a foot in a minute," replied Gus. "How long it
takes and how far the weight is lifted are just as important as the weight
itself. That's what horse-power is - a sort of combination measure of the
work done and the time it takes to do it. It doesn't make any
difference whether you lift 33,000 pounds one foot in a minute or twice that
weight half the distance in the same time. It still needs one
horsepower to do the job. But if you tried to yank 33,000-pound weight
up two feet in a minute you'd need two horsepower. Or if you could
take two minutes to move it up a foot you'd get by with only half a
horsepower."
"Now if you take it just by
itself," Gus explained. "A long time ago there was a bird named
Archimedes who got a lot of notoriety by claiming he could move the world if
somebody'd give him a long enough lever and a place to stand. Nobody
could call the old ducks bluff and he knew it, but he had the right dope
just the same. If you could go sailing out into space with a nice long
lever, hook the end of it under the earth, and rest it against any other
planet that happened to be handy, and you had some way to get a toe-hold on
the ether that's supposed to fill space, you could move this earth right out
of its orbit - provided the lever didn't bust. Old Archimedes wasn't
particularly interested in moving the earth anyhow - all he wanted was a
sensational way to explain how a crowbar works."
"What's that got to do with
horsepower of an auto motor?" asked Joe.
"A whole lot," Gus answered.
"A crowbar is nothing but a lever that fits the kind of power you have to
the job that has to be done. You can, for instance, push with a force
of one pound on the end of a lever and move it a distance of one foot.
With the right fulcrum - which is the point where the lever braces against
something solid - you can lift a weight of twelve pounds a distance of one
inch. Or you could move the fulcrum nearer the weight and find a point
where you could lift twenty-four pounds a half inch. An automobile is
just full of levers, only most of 'em aren't like crowbars. They're
gears, and gear really are continuous levers."
"Still I don't see the
connection between gears and horsepower," Joe objected again.
"You will in a minute," Gus
continued. "A gasoline motor is a lot like a human being in some
respects. With a lever you can lift a heavy weight that you couldn't
budge if you grabbed hold of it direct. The gasoline motor turns the
crank shaft with only so much turning force - called torque. So the
motor is speeded up and by means of gears this fast, not-so-strong motion is
turned into a slower movement with a lot of pull to it."
"Then it's the gears that
determine the pull, and the horsepower hasn't anything to do with it?"
Joe interrupted.
"If you're talking about
just plain pull, that's right. By using extra low gearing you could
drive a five-ton truck, fully loaded, up the side of a steep mountain with a
one-horsepower motor. Of course it would barely crawl along - you'd
have sacrificed speed to get the necessary pull."
"But couldn't you speed the
motor to beat the band to make up for that?" Joe suggested.
"Now you're getting into
some of the ins and outs of engine design," smiled Gus. "That's what
the engineers have been doing ever since the first gasoline engine was
built. Instead of making bigger and bigger cylinders to get more
power, they have let the cylinder size alone and obtained more power out of
the same set or cylinders by making 'em work faster. Bigger valves,
larger gas passages, higher compression, lighter moving parts, better
balance have all been used to let the motor turn over faster and still
develop the same turning force or torque. If you did all those things
to the one-horsepower motor in the five-ton truck we were talking about,
you'd make it go up the hill faster all right because the motor wouldn't be
a one-horse motor any longer. Maybe it would be as much as two
horsepower. Lots of auto motors rated at ninety to a hundred
horsepower today have no bigger cylinders than the forty- and
fifty-horsepower cars of years ago."
"I suppose that's why they
rate gasoline motors at a certain horsepower at so many revolutions a
minute," observed Joe. "Do those ratings tell how fast the motor will
run?"
"Not at all," Gus explained.
"All motors will turn over faster than the rate at which they develop the
most horsepower. Only, when the motor speeds up beyond that point, the
turning force drops off so fast that the horsepower goes down. It's
like running a foot race. You get going about so fast and when you try
to go any faster the muscles in your legs won't put any push into your
feet."
"Then that explains why
different cars have different gear ratios," Joe commented.
"Each one has a gear ratio
that will let the motor run at the speed where it will develop the most
amount of power."
"That's how they ought to be
geared," said Gus. "Actually they're not. It's a sort of a
compromise in most cases. Most everybody wants to be able to climb the
side of a house in high gear and pull through the toughest kind of going
without shifting. You can't have your cake and eat it, too, Joe, so if
cars have to be made for people too lazy to shift gears, the manufacturers
have to gear 'em lower than the best point for smooth easy running, maximum
speed, and best gasoline economy on level roads."
"Maybe that's why some of
the cars are fitting four-speed transmissions," Joe suggested.
"Sure, but if a driver is
too lazy to shift a three-speed transmission, putting four speeds in the box
isn't going to cure him," Gus grumbled. "A real four-speed
transmission would be ideal, but the ones they're fitting now are geared so
low on high they really amount to a three-speed outfit with first speed
reduced to an extra low gear that isn't any use."
"Wouldn't that extra low
first, if you had it in a hundred-horsepower car, make it pull like fifty
pairs of horses?" Joe asked again picking up the specifications of the car
that had started the discussion.
"It might if it were low
enough and you loaded the car with pig lead to give it traction," said Gus,
sweeping the crumbs off the table into his lunch kit. "No matter how
much power you've got or what the gear ration is, you can get only so much
pull before the back wheels of the car begin to slip. It sure would take a
lot of weight to make two rubber tires grab the road like four hundred
horseshoes!"
END
