Few things are sweeter than the sound of a well-tuned car engine. How does this cylinder-born symphony reach the driver?
Moving from the rural ages to the industrial, the sounds around us gradually progressed from the animal to the mechanical. Although never as versatile, scary or enjoyable as nature’s soundtrack, it nonetheless begs the question: is there something in the sound of an internal-combustion engine that could still appeal to our ears in this modern age of noisy cars, trains and planes?
This depends mostly on whether you are a enthusiast. If so, engines produce music as a by-product of the work they do for us. If not, an engine’s operation merely represents an intrusive noise. Since we mostly fall into the first category, let’s take a closer look.
All sound waves have an amplitude and a frequency or, more simply put, loudness and speed. So, the higher the amplitude, the louder; the greater the speed, the higher the pitch. When a variety of sound waves combine, harmonics are introduced, rendering the output far more aurally interesting. The resulting sounds, from different musical instruments, for example, are completely different to one another.
Can you tell what make of car, motorcycle, or aircraft is approaching from the sound? We might have to turn back the clock somewhat, because these days most cars sound similar, especially if they employ turbocharging. This is a pity because, in previous decades, there was a far greater diversity of sounds. Take the noise of an aircooled Beetle, for instance: very recognisable with its flat-four layout. Then, how about the distinctive beat of a BMW straight-six? A flat-six Porsche or boxer Subaru also have their unique sounds, while American V8s boast perhaps the deepest and best sound of all.
It’s even more prominent with motorcycles. The most recognisable is the engine sound of a traditional Harley-Davidson. You can’t confuse this with a Ducati, even though both are V-twins. The Ducati has 90 degrees between cylinders and the Harley only 45. This means the firing pulses have differing time intervals, resulting in the respective off-beat rhythms.
The deep drone of the nine-cylinder radial engine powering the North American T-6 Harvard used by flight trainers was a regular sound in our skies, while South Africa’s last remaining Shackleton also had a soul-stirring sound from its four Rolls-Royce Griffon engines. These were 60-degree V12 designs. But coming back to ground level, where are we today with car sounds?
In an effort to bring back the good old sounds, various methods are being employed. The closest to the original is to have a pipe with an openable flap that can emit the intake growl. This can be under the bonnet, or extended to the footwell for a bit more effect. Another trick is to use the car’s audio speakers.
BMW uses the audio system, while Ford employs a sound symposer with a tube feeding intake sound to the cabin. Some Volkswagen Group cars use a so-called "Soundaktor", a speaker device located under the windscreen. If not appreciated, these can easily be disconnected or adjusted using the OBD port (on-board diagnostics) and a relevant computer programme.
Toyota uses a sound pipe in its GT86 (with aftermarket kits available that can alter the sound effect based on the type of tube; they’re effective mainly above 4 000 r/min.)
A spin-off of using the car’s speakers is an exhaust sound simulation can be sent to the rear speakers, while an intake sound is directed to the front.
What can you do?
If your car is naturally aspirated, you could play with the exhaust system, or switch the fuel injection to old-school carburettors. If your engine is turbocharged, you are stuck with the same problem as the manufacturers (although Mercedes-AMG appears to have cracked the code). The best solution of all? Buy an old classic to tinker with.
Turbocharging is 'boring'
Forced-air induction has enabled viable downsizing of engines with some fuel economy benefits when you drive cautiously. From an aural standpoint, however, there’s a problem with turbocharging. When inlet air gets heavily accelerated and disrupted by the impellor blades, passes through the intercooler and then is forced into the cylinders, it leaves no discernible sound pattern through the inlet. At the other side of the turbo, the exhaust gases have to spool up the turbine blades, again disrupting and mixing the exhaust pulses and thereby removing any inherent sound characteristics. This is why many modern car engines sound more like a vacuum cleaner.
With a naturally aspirated engine using side-draught carburettors, you have short inlet manifolds. These tend to emit a deep sucking noise from each inlet pipe which can be quite impressive, even from a small four-cylinder engine. One example would be a classic Alfa Romeo, especially with a less restrictive air cleaner than standard.
In the days before catalytic converters, some of the most popular modifications were to the exhaust system. This was usually in the form of free-flow which allowed faster emission of exhaust gases. The complexity of fuel injection and emission systems now means such modifications are no longer popular and seldom beneficial.
Original article from Car