How to use this calculator
- Enter target power. Use crank or wheel power consistently with BSFC.
- Enter BSFC. Set fuel mass needed per unit power.
- Set injector details. Enter injector count, duty cycle, fuel density and pressures.
- Read flow rating. Review required cc/min per injector.
How it works
Fuel mass flow is power x BSFC. The calculator divides by injector count and duty cycle, converts mass flow to volume flow using fuel density, then corrects the required rating with the square root of pressure ratio.
Use the engine airflow calculator and BMEP calculator when checking whether the fuel target matches the engine airflow and torque target.
Worked example
Verified against the live calculator
A 300 kW gasoline target with 0.335 kg/kWh BSFC, eight injectors and 85% duty cycle needs roughly 265 cc/min per injector at the same rated and target pressure.
Frequently asked questions
What does the injector flow result mean?
It is the per-injector published flow rating in cc/min needed to support the entered power at the entered duty cycle and fuel pressure.
What BSFC should I use?
Use measured engine data when possible. About 0.335 kg/kWh is roughly 0.55 lb/hp-h, a common conservative gasoline estimate.
How does fuel pressure affect injector flow?
Injector flow changes with the square root of pressure differential ratio.
Is this for crank or wheel horsepower?
Either can be used if the BSFC assumption matches the same power basis.
Method & assumptions
- Flow correction uses square-root pressure scaling.
- Injector dead time, fuel temperature, regulator reference, transient enrichment and measured injector characterization are not included.