Enter your power target, engine type, and duty cycle to find the minimum injector flow rate required. Outputs in both cc/min and lb/hr.
Injector sizing is a function of three variables: how much fuel the engine consumes (BSFC × power), how many injectors share that load, and how long each injector can be open (duty cycle). Under-sizing causes lean conditions at high load - an engine-killing failure mode.
BSFC is how many pounds of fuel the engine burns per horsepower per hour. Naturally aspirated gasoline engines typically fall between 0.45-0.55. Forced induction engines run richer (higher BSFC) at peak load - use 0.55-0.65 for turbocharged builds, 0.65-0.70 for E85.
Duty cycle is the fraction of time an injector is held open. At 80% duty cycle, the injector is open 80% of each engine cycle. Running above 85% causes injector nonlinearity and poor atomization - the engine loses fuel control. Always size for 80% max as a safety margin.
Direct injection (DI) engines like the BMW N20, N55, and S55 have the injector spraying directly into the combustion chamber at very high pressure (200+ bar). Port injection injectors operate at 3-6 bar. These are not interchangeable - this calculator covers port injection sizing. DI injectors are rated differently by the OEM and cannot be swapped for larger units without ECU support.
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