I know how engines work, what makes them work etc. but this question has been on my mind for a while. How can a bunch of controlled explosions create the sound characteristic for a specific engine type? For example, a V6 engine sounds distinctly different than a V8 or I4, but how do they get their sound & why can’t the sound be different, for example an I4 engine with the sound of a V12?
In: Engineering
It’s important to keep in mind that ICE engines do not (unless there is something severely wrong!) create explosions. Think of it as a controlled burn.
As such, the sound you hear is a combination of sound waves interacting with each other as they leave the header and interfere. The number of cylinders, header design, and exhaust design all contribute to how this interference occurs.
The firing order of an engine can also determine its sound.
I.e. the v8 engines in german cars usually use cross plane crank shafts and have an even firing order allowing exhaust waves to flow smoothly one after another. Some american brands have uneven firing order and cause exhaust waves to collide and create either constructive or destructive interference. This results in the loud gurgling sound you hear from a classic v8.
The valve lift, cam profile, etc. can all also have an impact on engine sound.
The frequency harmonic differences between i4s, v8s, and v12s are due to the fact that as the engines increase cylinder count, there are (typically) more combustion cycles per rotation of the engine. So 3000rpm in an i4 engine has a lower harmonic than 3000rpm in a v12 (since there are 3 times the number of combustion cycles occuring per revolution).
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