Four Stroke & Cylinder Arrangements

What is a stroke?

The movement of the engine's piston inside the cylinder during each phase of the cycle.

What are the two types of stroke?

Upward, also called the compression stroke, and downward, called the expansion or power stroke.

What are the four stages of the four-stroke cycle?

Intake, compression, combustion and exhaust.

How many strokes does each stage correspond to?

One — each stage is one stroke of the piston, either upward or downward.

What happens during the intake stroke?

The piston moves down, creating a vacuum that draws a mixture of fuel and air through the intake valve into the cylinder.

What happens during the compression stroke?

The piston moves back up, compressing the fuel-air mixture and increasing its potential energy.

What happens during the combustion stroke?

A spark plug ignites the compressed mixture, which burns and expands rapidly, pushing the piston back down.

What is the combustion stage also called?

The power stage.

What happens during the exhaust stroke?

The piston moves up again and expels the burnt gases through the exhaust valve, clearing the cylinder.

What does the four-stroke cycle accomplish overall?

It turns chemical energy from the fuel into mechanical energy to power the engine and the vehicle.

What are the four common cylinder arrangements?

Inline, V, flat and radial.

What is an inline (straight) engine?

One where all cylinders are arranged in a straight line along the same plane, one after the other.

What are the advantages of an inline arrangement?

It is simple, compact and well balanced.

How many cylinders do inline engines typically have?

Three, four or six.

What is a V engine?

One where the cylinders are arranged in two separate banks, forming a V shape when viewed from the end.

Why are V engines popular for high-performance and larger vehicles?

They are compact and can accommodate more cylinders — six, eight, 10 or 12.

What is a flat (boxer) engine?

One where the cylinders are arranged horizontally in two opposing banks, with the pistons moving toward and away from each other.

What is the advantage of a flat engine?

A low center of gravity and smooth operation.

What is the drawback of a flat engine?

It can be more complex and takes up more space width-wise.

Which manufacturers commonly use flat engines?

Porsche and Subaru — usually in flat-4 and flat-6 configurations.

What is a radial engine?

One where the cylinders are arranged in a circle around a central crankshaft, with each piston connecting directly to the crankshaft.

Where were radial engines widely used, and why?

Early aircraft engines, because of their compact size and high power-to-weight ratio.

Are radial engines common in cars today?

No — they are less common in modern automotive applications.

What is firing order?

The sequence in which the cylinders ignite the air-fuel mixture to generate power.

Why does firing order matter?

It directly affects engine balance, smoothness, vibration and overall performance.

What does a proper firing order accomplish?

It distributes the load evenly across the engine components and ensures efficient power delivery.

What determines an engine's firing order?

The arrangement of the cylinders and the crankshaft design.

What is a common firing order for an inline-4?

1-3-4-2.

What is a typical firing order for an inline-6?

1-5-3-6-2-4.

Why does the inline-6 run so smoothly?

It has an inherent balance, and the firing order further reduces vibrations and harmonics.

What are common V6 firing orders?

1-2-3-4-5-6 or 1-4-2-5-3-6, depending on the engine design.

What are popular V8 firing orders?

1-8-4-3-6-5-7-2 and 1-3-7-2-6-5-4-8.

Where is an engine's firing order recorded?

Stamped or engraved on the engine block, cylinder head or intake manifold.

What happens if the firing order is wrong?

Engine damage, poor performance or excessive vibrations.