Injector Sizing
Injector flow for a target horsepower from the BSFC you enter, injector count and the duty you allow; flow at another pressure; cc/min at your fuel density.
Total fuel flow and the static flow each injector must deliver, in lb/h and cc/min, plus what a rated injector flows at your pressure and the duty it would run.
Example: 400 hp at 0.50 lb/hp·h needs 200 lb/h; over 8 injectors at 80 % duty that is 31.25 lb/h each — 328 cc/min at 0.72 g/mL.
Fuel per horsepower,
shared out.
How the fuel flow for a target power is derived from BSFC, how it is split over injectors and duty cycle, what pressure does, and why BSFC is yours to supply.
Flow from power
An engine burns fuel in proportion to the power it makes: fuel mass flow (lb/h) = horsepower × BSFC, the brake specific fuel consumption in lb per hp·h. Divided by the number of injectors and by the duty cycle you allow, that is the static flow each injector must deliver at wide-open, full-time opening. Halving the allowed duty doubles the flow needed.
BSFC and duty are yours
BSFC differs by fuel, aspiration, tune and the power point — a naturally aspirated petrol engine and a boosted E85 engine are far apart. This page does not assume a value; take it from dyno data or your tuner. The duty cycle headroom is likewise a tuning choice; 100 % means none was allowed for, and the page says so.
Pressure and volume
Injector flow scales with the square root of the pressure across it: a 30 lb/h injector rated at 43.5 psi flows 30 × √(58 ÷ 43.5) = 34.6 lb/h at 58 psi. Volume flow in cc/min needs the fuel’s density — 1 lb/h is 453.6 g/h — so cc/min is shown only when you enter a density, from the fuel supplier.
What the number does not settle
Crank horsepower is the basis; wheel figures need drivetrain loss added back. Injector dead time, minimum pulse width, fuel pump and line capacity, and the engine’s actual air–fuel targets are the tuner’s work. Inputs stay in your browser; the same four anonymous usage counts as the rest of the site apply.