What Is Engine Displacement? 5 Key Facts Explained

The word ‘displacement’ usually has a negative meaning, but in the motoring world—the more displacement the better. Engine displacement is a term relating to the combustion process of the vehicle, which generates the power to get the wheels moving. You might not have heard of the phrase before, but you’re likely to know plenty about it already.
It’s not something that can be altered easily, or requires repairs, but you’ll need to know about it for an auto mechanic career. Luckily it’s a pretty straightforward concept, so let’s take a look at five things you need to know about engine displacement.

1. Engine Displacement and the Combustion Process

Displacement is about what happens with the pistons and cylinders in the engine. Vehicles usually have four, six, or eight cylinders, each containing a piston which moves up and down during each stroke. These cylinders are fed with a mixture of air and fuel which is ignited by the spark plugs to create power for the vehicle. Engine displacement refers to the volume of the cylinders, which are developed in lots of different sizes by individual manufacturers. For example, the powerful engine in a Ferrari will have a much larger displacement than its equivalent in a small Honda.

Pistons during mid-stroke in the engine cylinders

2. How to Calculate Engine Displacement

If you’re interested in auto mechanic training, you’ve probably seen engine power referred to in terms of litres before. That’s the measurement of engine displacement, and it’s calculated using bore, stroke, and the number of cylinders. The bore is the diameter of the cylinder, and the stroke refers to the distance travelled by the piston between the top and bottom of the cylinder. The official calculation of engine displacement is a little bit complicated, but it eventually generates a reading in litres or CC.

3. The Effect of Engine Displacement on Vehicle Performance

The bigger the engine displacement volume, the more air that can be pushed into the cylinders. This boosts the combustion process and allows the engine to generate more power. This does, of course, have an obvious downside. Fuel efficiency is likely to drop when displacement increases, so drivers will have more frequent trips to the gas station. Low displacement engines are more likely to be found in family cars as a result, where power is less necessary.

4. Engine Volume Always Stays the Same

The total volume of the engine’s cylinders remains constant at all times, despite all the piston movement taking place. It’s one of the most fascinating parts of engine design, because no two pistons are ever at the same stage of the combustion process. One could be about to start its cycle, while the others are mid-stroke or completing their cycle. This synchronization keeps the engine volume the same throughout any trip in a healthy vehicle.

5. How Engine Displacement Affects an Auto Mechanic Career

Other than a full engine replacement, there’s nothing that a motorist can do to increase or decrease the displacement in their vehicle. It’s still a very relevant topic in automotive mechanic schools, though, because it could explain low fuel efficiency being experienced by a customer. Damaged pistons or cylinders are big problems for an engine and could warrant replacement of the entire block, so give it plenty of attention if you notice something worrying.