How injector sizing works
BSFC expresses fuel mass per horsepower per hour. Multiply power by BSFC, divide by injector count, then divide by the allowed duty-cycle fraction. At 80% duty an injector is open for 0.8 of the available time, so its rated flow must exceed average demand per cylinder.
flow(lb/hr) = hp × BSFC ÷ injector count ÷ (duty cycle ÷ 100)
Example for 300 hp
At 300 hp, 0.5 BSFC, four injectors and 80% duty, total demand is 150 lb/hr. Each injector needs 46.875 lb/hr rated flow at the relevant pressure. With density 0.745 g/cc, this is about 475.66 cc/min. The BSFC and density are example assumptions, not universal specifications.
What to check before choosing an injector
Compare ratings at the same injector pressure differential. Fuel, boost, mixture and load affect demand, while density depends on composition and temperature. This estimate does not check minimum pulse width, spray pattern, electrical compatibility, fuel pump capacity or ECU characterization. Direct injection needs a more specific injection-window model.