How the sound is made
No samples and no recordings. Each sound comes out of a small model that runs about 48,000 times a second on your own device.
1. The crank
The simulation keeps one number that matters most: crank angle. A four-stroke engine finishes a cycle every 720 degrees, two full turns. Each cylinder gets its own place in that cycle, set by the firing order.
A second layer works out how fast the crank should turn. Throttle sets manifold pressure, pressure sets how much charge each cylinder takes in, and charge sets torque. Friction, pumping losses, the clutch and the car on the other side of the gearbox all pull back. That is where idle, the rev limiter, stalling and shifting come from.
2. The pulse
When an exhaust valve opens, gas still at high pressure rushes out. That blowdown is a sharp pressure spike, followed by a lower push as the piston clears the cylinder. Its size follows the charge that cylinder burned. No two pulses match: each has a little random variation, more at idle, and each cylinder has a small fixed offset of its own.
3. The pipe
Every pulse enters a header with its own length, so unequal headers really do shift pulses in time. Then it travels down the exhaust as a two-way wave. The open end sends low frequencies back up the pipe, inverted, and lets high ones out. The result is a pipe that rings at a pitch set by its length. As the gas heats up under load, the speed of sound rises and that pitch climbs.
Engines with two exhaust banks get two pipes that do not quite match, as on a real car. Without that, the pulses would add back into an even train and you would lose the V8 burble on a mono speaker.
4. Everything else
- Intake: a short pipe that opens up with the throttle.
- Block: a few resonances struck by each firing. Diesels hit them much harder.
- Flow noise: the hiss of gas through the muffler.
- Turbo: a whine tied to shaft speed, with lag, and a blow-off when you lift.
- Afterfire: unburnt fuel popping in the pipe on the overrun, which rings the pipe like any other pulse.
5. The speaker
A phone speaker cannot play 40 Hz. The Phone sound setting splits off the low band and re-makes it as overtones the speaker can reach, and your ear fills in the missing bottom note. Headroom goes to what can be heard. Use Full on headphones.
What it is not
This is a toy model built to sound like an engine and respond like one. It is not a measurement of any real engine, and the dyno figures only describe the model.