Fuel Injector Size Calculator

When to use it

• Compare how a change in target power affects injector flow before committing to parts, setup, or strategy changes.
• Check a workshop, dyno, simulator, or trackside spreadsheet result using a transparent formula: Power × BSFC ÷ injectors ÷ duty cycle.
• Use the result with known fuel density, measured fuel pressure, realistic duty-cycle limits, and logged lambda data. Fuel systems should be sized with headroom because demand changes with boost, temperature, fuel type, and engine safety targets.

How to use it

1. Enter target power in hp; the default value shown is 500 hp.
2. Enter bsfc in lb/hp/hr; the default value shown is 0.55 lb/hp/hr.
3. Enter injectors as a plain number; the default value shown is 4.
4. Enter max duty cycle in %; the default value shown is 85 %.

How to read the result

Injector flow is shown in lb/hr each. Use the number as a calculated reference point, then compare it with measured data from the car, the part supplier, or the race environment. A mathematically clean answer can still be unsuitable if the inputs are estimated, rounded, measured under different conditions, or outside the normal range for the vehicle.

Assumptions and checks

• The calculator applies the displayed formula directly and assumes the entered target power, bsfc, injectors, and max duty cycle are valid for the vehicle and conditions being considered.
• Changing target power and bsfc together can move the answer in ways that are easy to miss, so make related setup changes deliberately.
• Confirm the fuel type and density when converting between mass flow and volume flow.
• Keep injector duty cycle and pump capacity below their practical limits with a sensible reserve.
• Verify fuelling changes on proper measuring equipment before relying on them at full load.