Fuel Pump Calculator
How many liters per hour your build needs, from power and BSFC - and the rail pressure the pump must still deliver them at, because the number on the box was measured somewhere easier.
Enter Your Build
Required Pump Flow
Your operating point, drawn
What margin buys
| Margin | lph | US gph | lb/hr |
|---|
The math, and what it assumes
Fuel mass is the physics: an engine making 400 hp at a BSFC of 0.65 lb/hp/hr burns 260 lb of fuel per hour, and the pump must move it. Volume follows from density - this tool uses 720 g/L for gasoline and 781.65 g/L for E85, the same values behind the injector size calculator and the ethanol blend math in the AFR lambda calculator, so the three fueling tools can never quietly disagree. BSFC itself is an assumption, not a measurement: the published bands are 0.45 to 0.50 naturally aspirated, 0.55 to 0.60 supercharged, 0.60 to 0.65 turbocharged, and this tool presets the top of each band because a pump sized for the thirsty end of the range fails safe.
Read the chart at your rail pressure, not the headline
The number printed on a pump's box is measured at free flow or low pressure, where every pump looks generous. Your engine does not run there. With boost and a 1:1 manifold-referenced regulator the rail sees base pressure plus boost - 58.5 psi for a 43.5 psi base and 15 psi of boost - and pump flow falls as the pressure it works against rises. Two pumps with the same headline can differ by a third at 60 psi. This calculator cannot know any specific pump's curve, so it gives you the required flow and the pressure to look it up at: find the manufacturer's flow-vs-pressure chart and check that the curve still clears your number there. A pump with no published chart at all is itself a signal.
Voltage is the quiet second derating
Flow charts are recorded at about 13.5 V at the pump terminals. A tired ground or a factory wiring path can leave a running car at 12 V, and pump flow drops meaningfully with it - often by 15 to 25% at pressure. If the manufacturer publishes a 12 V curve, size against that one; if the build is serious, a relayed feed with proper wire gauge recovers flow more cheaply than a bigger pump.
E85 asks for more, but less than you have heard
The injector rule of thumb says E85 needs 30% more flow, and this tool applies exactly that rule to fuel mass, matching the injector size calculator. But a pump chart measures volume, and E85 is about 9% denser than the 720 g/L gasoline reference, so the volume requirement lands about 20% above gasoline rather than 30. Both numbers are honest; they measure different things. What the turbo is asking the fuel system to feed in the first place is a question for the boost to horsepower calculator.