In this video we are going to cover the core concepts of 4 stroke cycle,

engine capacity, torque and power.

The most common kind of car engine is the 4 stroke engine

named after the 4 strokes the piston must travel

to complete 1 cycle of combustion.

These 4 strokes are affectionately known

as suck, squeeze

bang and blow

The first stroke moves down the piston

while a fuel/air mixture is sucked into the combustion chamber.

The second stroke moves the piston up the cylinder again

compressing the mixture.

The third stroke starts with a bang

as the spark-plug ignites the compressed, explosive mixture.

The expanding gas from this explosion pushes down the piston

and thus generates power.

The fourth and final stroke moves the piston up

pushing the exhaust out of the combustion chamber.

During this cycle,

the exhaust and intake valves open and close

at appropriate times to allow for fuel mixture intake,

its compression,

and exhaust to be blown out.

Engine sizes are generally measured in capacity.

Either in litres

cubic centimeters

or cubic inches

An engine’s capacity is the maximum volume for each cylinder,

multiplied by how many cylinders the engine has.

This is an example with a 2-litre Inline-4 engine.

Here, the four cylinders each have a maximum volume of half a litre.

Larger capacity engines have the potential to make more power,

but they will normally use more fuel.

This is due to to the extra friction caused by the larger surface area

of the engine’s internal components.

There are two distinctly different measurable quantities an engine produces:

power and torque.

You can think of torque as how strong the explosions push against the pistons,

power is a combination of how big the explosions are

and many happen per second.

Power is the only useful measure of how hard the engine can accelerate a car.

Torque just helps describe how that power is delivered.

Power is the measure of how much work is done per second.

Torque is the measure of force.

I’ll give you an example in the form of a problem

commonly faced by us Australians:

Your mates Stevo and Robbo

have to move 8 slabs of beer from the tray of Robbo’s ute to the shed.

Robbo decides to carry 4 slabs at once.

This makes him pretty slow so he takes 4 minutes to get to the shed.

Stevo decides the best way is to carry 1 slab at a time,

but run to the shed as fast as he can.

This only takes him 1 minute to go the the shed and back.

They both do the same amount of work,

moving 4 slabs in 4 minutes,

thus they both make the same power

but they have two different ways of doing it.

Robbo uses lots of strength but walks slowly.

He is a high torque, low RPM engine.

Stevo uses less strength, but runs a lot faster.

He is a low torque, high RPM engine.

A different perspective is to see an engine as an air pump.

To make more power you need to pump more air.

This can be done by having a bigger capacity,

sucking in more air with every stroke,

giving you stronger bangs and more torque,

or by making the engine run to a higher speed

sucking in more air every second,

making more bangs every second,

which makes more power from the same amount of torque.

Engines, like most things, are a series of trade-offs.

Making more power from an engine might come at the expense of worse fuel economy,

higher emissions

and lower durability.

Your job will be to produce engines suitable to your desired application.

This could be anything from supercar engines that live fast and die young,

to a long lasting, durable family car motor.