How the number of cylinders effects engine behaviour

In its simplest form, an engine has a single cylinder, although this is not suitable for motor car applications as the torque would be very uneven due to the fact that there is just one power stroke for every two crankshaft revolutions and the vibration that would occur as a result. This design is however commonly used in motorcycles and some microcar applications. One example of which is the Villiers engine as shown below;

The minimum amount of cylinders required to provide acceptable levels of vibration and harshness in motor cars is two, giving one power stroke per crankshaft revolution although, compared to engines with larger numbers of cylinders, the vibration at low speeds is still very much noticeable. In the case of a single-cylinder engine, even a large flywheel designed to store this energy would be inefficient in giving smoother running at lower speeds. 

Motor vehicles today use typically anything from 2 to 12 cylinders, all of which can be arranged in a number of ways. The average torque value of a four-cylinder engine will be greater than that of a single-cylinder engine of the same displacement however, the maximum torque value generated by each individual cylinder would be significantly lower than that of a single cylinder engine of the same displacement.

Torque delivery is much smoother with multi-cylinder engines owing to that fact that the more cylinders an engine has, the more power strokes per crankshaft revolution. Multi-cylinder engines also have the added advantages of being safer at higher speeds, a greater ability to develop more power and have longer lives due to less uneven torque and vibration. Although multi-cylinder engines are essential for smooth running in motor car applications, there is the obvious drawback of the fact that they are more complicated in their design due to the increased number of parts and overall cost of manufacture.

Traditionally, more cylinders meant more power however nowadays, manufacturers are continually moving towards the trend of smaller engines due to emissions laws. Thanks to modern technology, smaller engines can now produce much higher power outputs and it is not unheard of for these aforementioned engines to produce more power than older engines of more than twice their size or capacity.

In certain cases, high-performance supercars have now taken to using W-engines, incorporating up to 18 cylinders

A W16 engine of the Bugatti Veyron