Calculators · Engine
Firing interval and engine frequency calculator
How often an engine fires shapes how smooth it feels, how it sounds and which vibrations it produces. These calculators give the crank angle between firing events for any cylinder count, the firing frequency at a given speed — the dominant tone in the exhaust note and a key figure in vibration diagnostics — and a straight conversion between RPM and hertz.
Firing interval in crank degrees
Divides the degrees of one full engine cycle by the number of cylinders. An even interval means evenly spaced power pulses; engines that differ from it, such as some V-twins, are called odd-firing.
interval = 720° / cylinders (four-stroke) interval = 360° / cylinders (two-stroke)
Firing frequency
Counts combustion events per second at a given speed. This frequency dominates the exhaust note and is the main excitation order engineers look for when chasing vibrations.
f = (rpm / 60) × cylinders / (2 for four-stroke, 1 for two-stroke)
RPM to frequency
Converts rotational speed into cycles per second and the time for one revolution. Useful for vibration analysis, sensor signals and matching a sound to a shaft speed.
f = rpm / 60 T = 1,000 / f (milliseconds)
Worked example: a V8 at 6,000 rpm
- Firing interval: 720° / 8 = 90° of crank rotation between power pulses.
- Crankshaft frequency: 6,000 / 60 = 100 Hz.
- Firing frequency: 100 Hz × 8 / 2 = 400 Hz — the fourth engine order.
Even firing intervals of common engine layouts (four-stroke)
| Cylinders | Firing interval | Engine order |
|---|---|---|
| 1 | 720° | 0.5 |
| 2 | 360° | 1 |
| 3 | 240° | 1.5 |
| 4 | 180° | 2 |
| 6 | 120° | 3 |
| 8 | 90° | 4 |
| 10 | 72° | 5 |
| 12 | 60° | 6 |
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About these results
Results are theoretical estimates from standard engineering formulas. Real-world figures depend on conditions these formulas do not capture. Always follow the manufacturer's specifications for maintenance, loading and safety decisions.
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