Enter your Engine RPM, Injector Pulse Width, Number of Cylinders, and Induction Type into the Fuel Injector Duty Cycle Calculator to find your Injector Duty Cycle — plus Engine Cycle Time and Injection Frequency so you know exactly how hard your injectors are working.
Injector Duty Cycle
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Engine Cycle Time
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Injection Frequency
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Fuel injector duty cycle (IDC) is the percentage of time the injector is powered or activated during an engine cycle. It's calculated by dividing the injector pulse width by the total cycle time and multiplying by 100.
Most tuners recommend keeping duty cycle below 80-85% for safety. Running at 90-95% duty cycle leaves little margin for error and can cause fuel delivery issues, especially under varying conditions.
As RPM increases, the engine cycle time decreases, so the same pulse width results in a higher duty cycle percentage. This is why high-RPM engines often require larger injectors to maintain safe duty cycles.
Pulse width is the amount of time (in milliseconds) that the fuel injector is opened and spraying fuel. It's controlled by the engine ECU and varies based on fuel requirements.
Monitoring duty cycle helps ensure your injectors can supply adequate fuel at all RPM ranges. High duty cycles indicate you're approaching injector limits and may need larger injectors.
Engine cycle time = 120,000 / RPM (in milliseconds). This represents the time for one complete engine cycle including intake, compression, power, and exhaust strokes.
Induction type doesn't directly affect duty cycle calculations but influences fuel requirements. Turbocharged and supercharged engines typically require higher fuel flow and may operate at higher duty cycles.
Duty cycles over 100% are impossible as the injector cannot be open longer than the engine cycle time. High duty cycles (above 90%) indicate insufficient injector capacity for the fuel demands.