Fuel Injector Sizing Calculator

Injector flow rate from engine HP and fuel type.

Target HP

Number of injectors

BSFC (lb/hp·hr)

Max duty cycle (%)

Fuel pressure (PSI)

Tab to move between fields

Injector size (cc/min)

361

Injector size (lb/hr)

34.4

Total fuel flow (lb/hr)220

Fuel consumption (GPH)36.2

Duty cycle at target (%)80

Max HP at 100% duty500

Pressure correction1

Injector count8

How to Use This Calculator

How the result changes with Number of injectors

Target HP: Target wheel horsepower the injectors need to support.
Number of injectors: Number of fuel injectors (typically matches cylinder count).
BSFC (lb/hp·hr): Brake-specific fuel consumption. NA gas: 0.45-0.50, turbo gas: 0.55-0.65, E85: 0.65-0.75.
Max duty cycle (%): Maximum safe sustained duty cycle (80% recommended, 85% aggressive).
Fuel pressure (PSI): Operating fuel rail pressure. Most port injection: 43.5 PSI, returnless: 58 PSI.

Injector size (cc/min): Minimum injector flow rate needed in cc/min (rated at 43.5 PSI base).
Injector size (lb/hr): Minimum injector flow rate needed in lb/hr.
Total fuel flow (lb/hr): Total fuel demand across all injectors at target HP.
Fuel consumption (GPH): Total fuel consumption in gallons per hour at target HP.
Duty cycle at target (%): Injector duty cycle at target HP with selected injector size.
Max HP at 100% duty: Absolute maximum HP these injectors can theoretically deliver.
Pressure correction: Flow correction factor for non-standard fuel pressure.
Injector count: Number of injectors used in the calculation.

Identify Input Parameters
4 parameters
Target HP = 400, Number of injectors = 8, BSFC (lb/hp·hr) = 0.55, Max duty cycle (%) = 80 = 5 input(s) provided
Calculate Injector size
361 = 361
Calculate Injector size
34.4 = 34.4
Calculate Total fuel flow
Total fuel flow = targetHp * bsfc
220 = 220
Calculate Fuel consumption
Fuel consumption = totalFuelFlow / 6.073
36.2 = 36.2