Torque vs Horsepower | How It Works


– Drag Racing! NASCAR! Rally! Racing! Awesome cars make awesome power. You know how we compare em; with stats. But what’s it really mean? We’re about to find out. We’re talking about horsepower and torque. (trap music) The way Tony talks about
it, torque is a grunt, (grunts) and horsepower is screaming. Torque and horsepower are
both ways of measuring force. Torque measures twisting force, and horsepower measures work, and work is force over time. So let’s start with torque. (grunts) You’ve probably heard of foot pounds. Pound is a measure of force. If you weigh 180 pounds,
that’s because your mass, what you’re made of is
exerting 180 pounds of force on the earth. A foot pound is a pound of force amplified by a foot of leverage. This is Jesse’s toolbox, and this is a weird bolt in a board. This is a wrench. (soft piano plays) If I use a foot-long wrench, and apply one pound of force at that bolt, I’m applying one foot pound
of torque on the bolt. If I used this two foot bolt buster, and apply one pound of force at this end, I’m applying two foot pounds of torque. If I apply two pounds
of force at one foot, it’s force on the bolt is the
same as one pound of force from two feet. Two foot pounds, or pound feet. It’s the same unit because it’s math. The distance from the point of measurement amplifies the force through the lever arm. I wonder where it all goes. (yells) Engine torque measures
the amount of this force that an engine can produce. Let’s get inside there. The pistons drive this crank shaft. You can see that where it attaches turns around the center axis. Just like the wrenches
turned around the bolt. Each explosion in the
cylinder pushes the piston down with force. That force is exerted on the crank pin, and transferred to the
shaft to get it spinning. Torque is determined by two factors. The amount of force on the crank pin, which comes from the piston, and the distance of that
force from the center axis, or throw, which varies by crank shaft. Make sense? If the throw stays the same, we produce more force from the piston. Maybe with more displacement
we can increase the torque. If the force from the
piston stays the same, we can increase the distance of the pin from the crank shaft center
to increase the torque. There’s millions of
combinations and variations that we can tweak to adjust the force exerted on the crank shaft. From the number of cylinders, to the shape of the engine, even to the type of fuel we use, which we can get back to in a minute. Horsepower is a measurement of work, and work is force over time. James Watt lived from 1739 to 1819 and he loved doing math. Steam engines were changing everything during the Industrial Revolution, and Watt wanted to give
people a way to measure all of the work that was getting done. Watt was watching work ponies, which are not tiny horses. Ponies are their own thing. You can look it up. Fact: he noticed that a
pony took about a minute to raise 220 pounds of coal
out of a hundred foot well, and being a scientist
he increased that number by 50 percent because a horse
is about 50 percent bigger than a pony. Whatever. It’s a unit. As long as it’s consistent,
it can be whatever he wanted. He figured that one horse
could do 33,000 foot pounds of work every minute. A horse, exerting one horse power, can raise 330 pounds of
coal 100 feet in a minute, or 33 pounds 1,000 feet in a minute, or a 1,000 pounds of
coal 33 feet in a minute. That’s work. That’s horsepower. The amount of force. Foot pounds. Torque produced over time is horsepower. Because torque is how much
force an engine produces, horsepower is how quickly it
can produce how much force. We can dive into this by
looking at how we measure car horsepower on a dynamometer. You can either put the car on a roller that’ll measure the force
produced at the wheels, or if you attach shaft to an engine you can measure the driving
the shaft and it’s speed. Start your car. You put it in neutral and floor it. Well the engine would
run so fast it’d explode. A dynamometer finds a
load to the floored engine and measured the speed it moves. You can hook an engine
to the dyno, floor it, and use the dynamometer to apply enough of a load to the engine to keep it at, say 7,000 RPM. You record how much load
the engine can handle then you apply additional load to knock the engine
speed down to 6,500 RPM and record the load there, then even more to get
it to 6,000 and so on. You can do the same
thing starting at 500 RPM and then work your way up. What the dynamometer is
actually measuring is torque, and because of math, to
convert torque to horsepower you just multiply the torque by the RPM and divide it by 5,252. That’s horsepower. Why 5,252? Well I’m glad you asked. You remember the horse? from before? With the coal. Okay. That horse moved 330
pounds 100 feet in a minute. So 33,000 foot pounds
of work in one minute is one horsepower. Now for my dumb brain Let’s use a hundred pounds, 330 feet in one minute, because that’s also one horse power. We need to show 330 feet
in one minute as revs, so let’s think of the wheel. The distance traveled on one revolution would be two pi r, or six
point two eight three one six. 330 feet in revolutions is 52.52. Starting to look familiar? A hundred foot pounds at
52.52 RPM is one horsepower, therefore one foot pound at 5,252 RPM is also one horsepower. So you take the torque,
multiply it by the revs and divide by 5,252 and
you found horsepower. (yells) (breathes briskly) When you plot horsepower versus the revs per minute for the engine, you get a curve like this one. An engine has peak torque where
it generates the most force. It has peak horsepower where
it produces the most torque most quickly. When you’re trying to accelerate quickly you wanna try to keep the engine close to it’s maximum
horsepower point on the curve. That’s why you downshift to accelerate. By downshifting you get
closer to the peak horsepower on the curve. You wanna launch your car from a stop? You rev engine right at peak torque then you release the clutch
to dump maximum power to the tires. Let’s take a minute to
talk about why diesel makes more torque but not much horsepower. Think about what torque is. Remember the long wrench? Well diesel has a much
higher compression ratio. Which means that the head of
the piston can travel further in the cylinder. That means the distance from
the center of the crank shaft can be greater. That means more torque but because the throw is
greater it’s got more distance to travel to get through a revolution so it can’t move as quickly and because horsepower
is work done quickly diesel engines can do a lot of work but not as quickly as as a gasoline engine when it’s cranking at high revs. That’s horsepower versus torque. Hit that subscribe button. It means a lot. Thanks to Audible for
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five hundred five hundred. You can do it with Audiobooks. The more people subscribe to Donut the more cool stuff we get to do for you. I love reading your comments. Let me know what you wanna see. Please like the show page. You like horsepower and torque check out James driving the Dodge Demon, or check out this wheelhouse on F1. Follow me on Instagram at @Bidsbarto. Follow Donut at @Donutmedia. Don’t tell my wife that’s Jesse’s toolbox. She thinks I can fix things.

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