Every sound here is synthesized live from four numbers: rpm, air charge, throttle and turbo state. No samples. Start the engine, then hold Space or drag the pedal.
Where the engine sits in rpm × air charge. Throttle and load move you vertically; the dashed line is the most air the engine can take in at each rpm.
Waveform (top) and spectrum, 20 Hz–10 kHz on a log scale (bottom). Watch the firing pulses stack into harmonics.
A crank phase runs over the 720° four-stroke cycle. Each time it passes a cylinder’s firing angle, a short exhaust pressure pulse starts: a fast blowdown spike that decays over the exhaust valve’s open time. Pulse height is the air charge in that cylinder, with a little cycle-to-cycle randomness that grows at light load, which is why idle sounds lumpy and full throttle sounds solid.
The firing angles and which exhaust bank each cylinder feeds are the whole recipe. A crossplane V8 sends uneven 90/180/270° gaps to each bank, which is the burble. A flat-4 with unequal headers delays every other pulse by a couple of milliseconds, which is the rumble. A 45° twin fires at 0° and 405°, then waits.
Each bank feeds a delay-line waveguide whose length is the pipe’s round trip at the speed of sound in hot gas, with an inverting, lossy reflection at the open end. That gives the pipe’s organ-like resonances. A low-pass muffler, a chamber resonance and soft saturation that drives harder with air charge follow.
Acoustically, “load” means how much air is in each cylinder, the same thing an ECU calls calculated load. Throttle opening, rpm and boost set it; external load only changes how fast rpm moves for a given throttle. On the dyno you can hold rpm and sweep throttle to hear the difference.
The same pulse train, band-passed around an intake resonance, plus pulse-gated airflow noise that opens up with the throttle. Small valvetrain clicks ride on each firing event. These dominate from the engine bay.
Shaft speed spools toward a target set by exhaust flow, with lag set by turbo size. Whine is a tone tracking shaft speed; whoosh is filtered noise scaled by boost. The turbine also smooths exhaust pulses, so the exhaust gets darker. Lifting under boost fires a blow-off valve (a downward-swept noise burst) or, without one, compressor flutter.
Closing the throttle above idle cuts fuel, but the pistons keep pumping a full cylinder of air through the exhaust on every stroke, so you hear a hollow stream of puffs plus hiss past the closed throttle, while the engine body keeps whirring with rpm. For a moment afterwards some of them fire in the exhaust instead, as pops with a crackle tail. The rev limiter cuts spark on most cycles, giving the classic stutter.