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Cars are able to unify people from different walks of life like few other things can. From great darers such as Ken Block, to journalists such as Jeremy Clarkson, to tuners such as Antonio Calvo, to the countless enthusiasts and engineers all over the globe, the car community is unique because of its variation. Some are designed to go fast around a track while others are designed to launch over dunes at high speed. However, there is also a sense of unity within the car community because cars represent more than just a metal frame with mechanical parts that drive four wheels while people sit inside going from point A to point B.
If there is one common identifying factor for car enthusiasts, it is to have a car with character. A key element of this is to have a car which makes all kinds of sounds. Every “pop,” “bang,” or “whoosh” from a car’s engine adds to the driving experience. It not only allows but encourages the driver to become one with their car. Some cars are well known purely because of how good their engine sounds.
One common way of characterizing a car’s engine is by its method of aspiration. In order to perform combustion, an engine needs to draw in air and mix it with highly atomized fuel and ignite it. Normally, air is drawn in from outside through an intake and brought into the combustion chamber. However, some engines use external devices such as turbochargers and superchargers to bring in even more air (a.k.a. forced induction). In any case, different components make different sounds. Each of them are quite unique.
A “naturally aspirated” engine is when an engine has no external devices to introduce additional air in the combustion process. This means that the primary source of noise from an engine is from the series of pressure waves that are generated after several combustion events in succession.
This means that as the rate of Revolutions per Minute (RPM) increases, the higher frequency these combustion events are. Hence, the engine tends to produce a higher exhaust note. Additionally, since engines produce more energy per unit time at higher RPMs, the amplitude of these pressure waves increases drastically. This is why engines are louder at higher RPMs. The exhaust system also plays a huge role as to which of these frequencies get amplified. We will cover this more in the next section.
Two examples of naturally aspirated engines that have vastly differing sound characteristics are big American V8s and F1 engines. In order to characterize their differences, we will take a look at the cross section of a basic internal combustion engine:
The most important piece to look at here is the cylinder. Specifically, we take its length into consideration. The longer it is, the longer the piston has to travel for every stroke. At high RPMs, this increases the likelihood of something going wrong. This is exactly why F1 engines are able to rev so much higher than Classic American V8s (This is also why their displacement is so much smaller comparatively).
As a result, F1 engines have a tendency to produce a scream-like exhaust note in their upper rev ranges while American V8s tend to produce a roaring sound.
Turbochargers are pretty clever devices. They utilize exhaust gases from an engine to spin a turbine. This turbine is connected to a compressor wheel, which helps the turbocharger take in more outside air from a separate intake and feed it into the combustion chamber.
Here is a cross-section of a turbocharger:
Image Credit: Schwitzer
Turbochargers have been known to increase fuel efficiency while outputting more power at higher RPMS. This has allowed many manufacturers to downsize their engines in a society with ever-changing emissions standards.