The Fuel Pump Horsepower Calculator takes a pump’s rated flow, the fuel’s specific gravity, a BSFC figure, and a usable duty limit, then returns the crank power that flow can feed.
Estimate Supported Crank Horsepower From Pump Flow, Fuel Density, and BSFC
This fuel pump horsepower calculator turns a pump’s rated flow into the crank power it can feed, using fuel specific gravity, BSFC, and a usable duty limit. Racers sizing a fuel system, tuners checking an existing pump, and E85 converters use it before buying pumps or injectors.
What to Enter From the Pump Datasheet and Fuel Spec
Pick Imperial (GPH, HP, lb/HP·hr) or Metric (LPH, kW, kg/kW·hr). Switching resets flow and BSFC to that system’s defaults. Enter pump flow, BSFC, fuel specific gravity as a ratio, and the usable duty limit as a percent. Every output follows the system you picked.
How Pump Volume, Fuel Density, and BSFC Set the Power Ceiling
Pump flow is a volume. Power comes from fuel mass. Specific gravity links the two. In Imperial, density is $8.33 \times SG$ in lb/gal, so the 0.74 default gives 6.16 lb/gal. Enter 0.72 instead and you get 6.01, the nominal weight of gasoline used in Performance Automotive Engine Math. In Metric, density is just SG in kg/L.
$$\dot{m} = Q \times \rho \qquad HP_{max} = \frac{\dot{m}}{BSFC} \qquad HP_{safe} = HP_{max} \times \frac{Duty}{100}$$
BSFC is a convention, not a standard. Aeromotive lists 0.60 to 0.75 for supercharged gasoline. The 0.50 default sits at the naturally aspirated end of that range. One input mistake wrecks everything downstream: entering the pump’s advertised free-flow rating. Pumps are rated at one test pressure and one voltage. Flow drops as system pressure climbs and as alternator voltage sags under load. Enter flow at your base pressure plus boost.
Flow must be at least 10 in the selected unit. BSFC runs 0.1 to 1.5, specific gravity 0.5 to 1.2, and duty 1 to 100 percent. Go outside those and the results clear, replaced by the halted warning. There is no upper limit on flow, so a mistyped 6,700 GPH returns a number without complaint. At 100 percent duty the result is the pump’s static capability with no reserve left for hot fuel, voltage drop, or a dirty filter.
Why the Flow Number Depends on System Pressure
How the Wheel Power and Airflow Rows Are Derived
Wheel power uses a fixed 0.85 multiplier. That is the 15 percent drivetrain loss convention, not a measured value for your car. Airflow uses 1.5 CFM per horsepower, the induction sizing convention quoted in carburetor and throttle body guidance. The metric 0.949 L/s per kW is the same figure converted, not a second rule.
$$WHP = HP_{safe} \times 0.85 \qquad Airflow_{CFM} = HP_{safe} \times 1.5$$
Do not read the airflow row as a carburetor size. It estimates what the engine has to breathe, not what a carburetor flows on its own test bench. The 0.85 factor never changes, whatever you drive. Automatics and all-wheel-drive cars usually lose more than 15 percent, so the wheel number reads high for them.
How the Injector Size and Track Consumption Rows Are Derived
The injector rows split usable fuel across four or eight cylinders at a fixed 80 percent duty cycle. That 80 percent figure is the maximum continuous duty widely cited for port injectors. The burn rows divide usable volume flow by 60.
Heat release uses 19,000 BTU/lb in Imperial and 44.4 MJ/kg in Metric. Both match the 116,090 BTU/gal lower heating value the DOE Alternative Fuels Data Center lists for conventional gasoline at roughly 6.1 lb/gal.
$$Injector = \frac{\dot{m} \times Duty/100}{N \times 0.80} \qquad Burn = \frac{Q \times Duty/100}{60}$$
Injector ratings depend on test pressure. Check whether yours is rated at 43.5 or 58 psi before buying to this number, or you will undersize the set.
Three assumptions are baked in and worth knowing. The Imperial injector row is a mass figure, so it moves with specific gravity. The Metric row is volumetric, so it does not. Raise SG and only one of them changes. The drain-time row also uses a 15-gallon cell in Imperial but a 60-litre cell in Metric.
Fifteen gallons is nearly 57 litres, so the metric run time comes out about six percent longer for the same setup. Heat release is fixed to gasoline as well. Enter methanol’s specific gravity and the mass flow changes, but the energy figure still reflects gasoline.
Input Mistakes That Distort the Supported Power Figure
Leaving a gasoline BSFC of 0.50 in place after switching to Metric, where the field wants kg/kW·hr and the equivalent is about 0.30.
Typing fuel density such as 6.16 into the specific gravity field, which exceeds the 1.2 ceiling and halts the calculation.
Switching measurement systems after entering values, which resets flow and BSFC to the defaults and discards what you typed.
Fuel Pump Sizing and Flow Questions Racers Ask
What duty limit should I enter?
Fuel system references commonly call for 15 to 20 percent headroom. That means entering 80 to 85 percent. The margin covers voltage drop, hot fuel, and flow lost to filters and lines.
Which specific gravity applies to E85?
E85 is denser than gasoline. Canton Racing publishes 6.59 lb/gal, which is about 0.79 here. E85 also needs a much higher BSFC, so change both fields.
Is the result crank or wheel power?
The main figure is crank power, because BSFC is defined against flywheel output. The wheel row applies the 15 percent loss separately. Do not subtract drivetrain loss twice.
Does fuel pressure appear in the math?
No. There is no pressure input. Handle pressure before you type: read the pump’s flow curve at your base pressure plus boost, then enter that number.
Why does a higher specific gravity raise supported power?
Denser fuel means more mass through the same volume flow, and power follows mass flow divided by BSFC. Denser fuels usually need a higher BSFC too, which cancels most of the gain.