Buzz
If you’ve read How Car Engines Work, you’ll know that engines are equipped with pistons, which move up and down within their cylinders. This motion is a key part of how the engine operates.
As the piston travels from top to bottom, it draws in a specific amount of air. The volume of air it takes in is determined by both the piston’s diameter and how far it travels during its up-and-down motion.
Imagine your car’s piston has a diameter of 4 inches (10.16 cm)—also known as the bore—and it moves 4 inches (10.16 cm) from top to bottom, which is called the stroke. This means that each piston in your engine can inhale the following amount of air:
5.08 cm (bore/2) ^ 2 * 3.14 * 10.16 cm (stroke) = 823.3 cubic centimeters
If your vehicle is equipped with 4 cylinders, the total engine displacement would be calculated as follows:
Typically, a car manufacturer will round this value and label the engine as having a 3.3-liter capacity. This means that the engine’s displacement is 3.3 liters. In practical terms, if you were to rotate the engine's crankshaft through two full revolutions, all four pistons would collectively draw in 3.3 liters of air.
So why does this matter, and why is there often a sticker on the back of many cars indicating the engine's displacement? The displacement serves as an estimate of the maximum power that the engine is capable of generating.
When gasoline mixes with air and ignites in the engine, there's a limit to how much gasoline can be added. This limit is determined by the amount of oxygen available—if you add too much gasoline, the cylinder won’t have enough oxygen to burn it. Typically, the air-to-fuel ratio is around 15 to 1, meaning 15 parts air for every one part of gasoline by weight. Displacement essentially tells you how much gasoline the engine can burn at most, which directly influences the engine's maximum power output.
While it’s certainly possible to design a 10-liter engine that performs poorly, and conversely, a 1-liter engine can be finely tuned for optimal performance, it’s important to note that both could have the same horsepower rating, even though the 10-liter engine has ten times the displacement. Generally speaking, though, a 10-liter engine should produce about ten times the power of a 1-liter engine, assuming all other factors are the same.
- Understanding How Car Engines Function
- The Science Behind Horsepower
- The Mechanics of Champ Cars – a detailed look into race car engines
- How Exhaust Headers Enhance Engine Efficiency
- What’s the Most Effective Way to Boost Engine Power?
