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Fuel Pump Flow Calculator

Enter target horsepower, BSFC and fuel density to size the required fuel pump flow.

Result

169.8 L/h
44.85 gal/h
275.0 lb/hr

How it is calculated

Mass flow is lb/hr = HP × BSFC, where HP is target engine horsepower and BSFC is in lb of fuel per horsepower-hour. It is converted to volume with L/h = lb/hr ÷ density, where density is in pounds per litre, and gal/h = L/h ÷ 3.785 (US gallons). If you leave BSFC empty the tool uses 0.5, and if you leave density empty it uses 1.62 lb/L, which is about 6.1 lb per US gallon, a typical value for pump gasoline. Horsepower, BSFC and density must all be above zero. Results are rounded to one decimal for L/h and lb/hr and two decimals for gal/h. The figure is the engine's demand at the stated power, not a pump rating, so size the pump above it.

Worked example

Target 500 HP, BSFC 0.55 lb/HP·h, density 1.62 lb/L. Mass flow: 500 × 0.55 = 275.0 lb/hr. Volume flow: 275 ÷ 1.62 = 169.8 L/h (169.75 before rounding). In US gallons: 169.75 ÷ 3.785 = 44.85 gal/h. So the fuel system must deliver about 170 litres per hour at full power, and a pump with extra headroom above that figure is the sensible choice.

Try this example →

Common mistakes

  • Entering density in lb per gallon (about 6.1) or in kg/L. The field is pounds per litre, so 6.1 would make the flow roughly four times too small.
  • Using a naturally aspirated BSFC for a boosted or high-power build. A turbo engine often burns more fuel per horsepower, so 0.45 can understate demand.
  • Entering wheel horsepower where the formula expects engine (crank) horsepower; drivetrain loss makes the crank figure higher.
  • Picking a pump whose rated flow equals the result. Pump ratings are quoted at a given pressure and drop under high pressure or low voltage, so a margin is needed.
  • Reusing the gasoline density for E85 or another fuel without changing density and BSFC; both differ noticeably.

About this calculator

Fuel pump sizing starts from how much fuel an engine actually burns to produce power, expressed as BSFC (brake-specific fuel consumption), typically in lb of fuel per horsepower-hour. Required fuel flow is simply target horsepower multiplied by BSFC, giving a mass flow rate that the pump and injectors must be able to deliver.

Because pumps and fuel lines are usually rated in volume rather than mass, that mass flow is converted to a volumetric flow using the fuel's density (roughly 6.0–6.3 lb/gal for pump gasoline, lower for E85), producing figures in L/h, gal/h and lb/hr that tuners compare against a pump's rated flow at system pressure.

Engine builders and tuners use this to avoid fuel starvation under boost or high RPM — sizing the pump with margin above the calculated demand (commonly 20–30%) so injector duty cycle and pump output stay safely within limits at the target power level.

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Comments (1)

  • Editorial team

    The tool sizes flow to the horsepower you want to make, so choose a pump that exceeds it with margin, as pump ratings drop with voltage and pressure. At 500 hp, 0.5 BSFC and 1.62 lb/L it gives 250.0 lb/hr, 154.3 L/h and 40.77 gal/h. Boosted or ethanol-fed engines burn more fuel per horsepower, so raise BSFC. What power level and fuel are you building for?

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