Multiply our 30-Hz value by three (the number of ignition events per crankshaft revolution for a six-cylinder engine) and you have the 90-Hz dominant frequency that defines the six-cylinder’s sound at 1800 rpm. Thus, a V-6 spinning at 1800 rpm can be said to be running at 30 Hz (1800/60 = 30).īut because a four-stroke engine fires each cylinder only once every two crank revolutions, we’re only worried about half the engine’s cylinders.
First, you convert engine rpm to Hertz, the frequency unit, with the following formula: 60 rpm = 1 revolution per second, or 1 Hz. They are all keyed to the engine’s rotational speed as revs rise and fall, the pitch goes up and down.Ĭalculating that dominant frequency at any given rpm is straightforward. These sound-generating vibrations derive from the combustion in each cylinder and the corresponding pressure waves in the intake and exhaust systems. A car’s engine under load plays a range of frequencies, but its root note-the pitch its musical chord is built on-is defined by its so-called dominant frequency. A higher frequency makes for a higher pitch, and vice versa. The frequency, or Hertz (Hz), of a sound wave-how many times the wave oscillates in a second-determines how our brain processes and interprets it as a distinct pitch. How can two six-cylinder engines sound so different?īefore we answer that, a brief primer on sound: It originates as vibrations that cause air-pressure disturbances that hit our eardrums. What separates a Porsche flat-six from a Toyota Avalon V-6-aside from the bank angle, the power output, the engine location, and your interest in owning one? At full throttle, the Porsche belts out an aggressive mechanical rasp while the Avalon mutters a nonthreatening burr.
#6 CYLINDER BOXER ENGINE DRIVER#
From the January 2015 issue of Car and Driver
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