- 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.
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Don't tell my wife that's Jesse's toolbox.
She thinks I can fix things.