Engine displacement, power and torque: what does each one do?

The technical specifications of an engine are full of technical data that we may not fully understand. This data helps us get to know the engine well and know what to expect from it and what specifications it has. Some of these terms, and possibly the most important ones, are engine displacement, power and torque. Do you know what these engine terms for your car mean? We explain them in a simple way so you know what each of these terms refers to.

Engine displacement

Engine displacement is one of those technical data points that becomes essential to know which engine our car has. To determine displacement, you need to know that each cylinder has two piston positions. When it reaches its highest possible point it is called Top Dead Center (TDC), and when it reaches its lowest level it is called Bottom Dead Center (BDC). The distance between both positions and the cylinder’s diameter gives us the unit displacement. It is measured in cubic centimetres.

Adding the unit displacement of all cylinders gives us the total engine displacement. For example, if each cylinder has a displacement of 500 cc and the engine has four cylinders, the total displacement will be 2,000 cc. This is usually referred to as a 2.0-litre engine, since 1,000 cc equals 1 litre of capacity.

Displacement is important for generating power. The greater the displacement, the more power the engine will generate. Burning more fuel requires more air, and the greater the displacement, the more torque the engine will generate and, consequently, the more power it will have. Some cars use a turbo or a supercharger to increase the air pressure in the cylinder, so they need less displacement to obtain greater torque.

Power

Engine power is measured in kilowatts (kW), although it is more commonly shown in metric horsepower (CV). It measures the force needed to cover a distance. For example, if an object is moved 1 metre in one second, a force X is applied, measured in newtons or joules. If that displacement is done in half a second, the distance is the same, but the applied force is doubled.

Power provides the speed needed to carry out the movement, using the force provided by the torque. It is calculated by multiplying the torque by the engine’s revolutions per minute, and in this way we obtain the kW or CV the engine delivers at specific revolutions per minute.

Torque

This is perhaps the least known technical term, but it is closely linked to engine power. Torque is the force applied in relation to a distance. It is measured in newton-metres and is quite simple to represent so that we can understand it. Imagine a nut we want to tighten. We can do it by hand, but there will come a point where, applying the same force, we can no longer tighten it further.

However, if we use a spanner, applying the same force, we can turn it further. The greater the distance between the point where the force is applied and the pivot point (in this case, the nut), the greater the effect. In the engine, this translates into the force the piston exerts as it moves down, transmitting it to the connecting rod connected to the crankshaft.

The torque can be modified by changing gears. If a small gear transmits its force to a larger gear, the torque is greater but speed is lost. If the gear transmits the force to one of the same size or smaller, the torque will be lower but speed will be gained.

To tow a trailer, for example, more torque is needed to cover the same distance with the same efficiency. The figures for torque and power are related, although torque is more important than power, since it represents the ability to do the required work—in this case, pulling a weight of X kg. Power, then, represents the speed at which that work can be done.

These concepts are more complex, but we show them to you in a simplified way so you can see what they represent and what they mean for your car.