Injector Duty Cycle Calculator
Calculate fuel injector duty cycle at target horsepower to verify injector sizing and avoid fuel starvation � critical for high-performance and forced-induction builds.
Results
What is it?
Injector duty cycle (IDC) is the percentage of time an injector is open during each engine cycle. An IDC of 80% means the injector fires for 80% of available time. Above 80�85%, the injector cannot close fully, losing precise fuel control and risking a lean condition � a potentially engine-destroying outcome.
How to use
Enter your target horsepower, number of injectors, brake specific fuel consumption (BSFC � a measure of engine fuel efficiency), injector flow rate in cc/min (stamped on the injector or in the datasheet), and target AFR. The result tells you whether your current injectors can safely support the power level.
Example scenario
A 300 HP engine with 4 x 550 cc/min injectors at 0.5 BSFC: total fuel flow = 150 lb/hr = 6,289 cc/min total, or 1,572 cc/min per injector. Duty cycle = 1,572 / 550 = 286% � far over 100%. You actually need injectors rated at minimum 1,572 / 0.80 = ~1,965 cc/min each, or more injectors.
Pro tip
Target a maximum IDC of 80% at peak power to maintain a safety margin. Always use injectors rated at least 25% above the calculated requirement. Note that injector flow ratings are at a specific fuel pressure (typically 43.5 psi / 3 bar) � increasing fuel pressure increases flow proportionally to the square root of the pressure ratio.