Fuel Pump Flow Calculator
Enter your peak horsepower and fuel to see how much fuel the engine burns at full power, in gallons and liters per hour. That's the minimum flow your fuel pump has to deliver at your fuel pressure.
How to calculate fuel pump flow
Fuel used (lb/hr) = horsepower × BSFC
Gallons per hour = lb/hr ÷ 6
Liters per hour = lb/hr ÷ 1.6
Horsepower times BSFC gives the pounds of fuel the engine burns per hour at peak power. Dividing by the fuel's weight turns that into volume: a gallon of gasoline weighs about 6 pounds and a liter about 1.6 pounds, the figures used in Summit Racing's fuel pump sizing guide. The calculator uses the gasoline weights for every fuel choice.
BSFC, or brake specific fuel consumption, depends on the fuel and whether the engine is naturally aspirated or boosted. The fuel injector size calculator has the full BSFC table.
Example: a 500 hp engine
A naturally aspirated 500 hp engine on gasoline, at a BSFC of 0.5:
500 × 0.5 = 250 lb/hr
250 ÷ 6 = 41.67 gallons per hour
250 ÷ 1.6 = 156.25 liters per hour
Adding a safety margin
The calculator's result is what the engine burns at peak power, with no margin added. A pump rated at exactly that flow would run flat out at full throttle with nothing in reserve.
To leave headroom, divide the result by the share of the pump's flow you want the engine to use. Dividing by 0.8 sizes the pump so the engine uses no more than 80% of it, the same 80% the injector calculator uses for duty cycle. For the 500 hp example that's 41.67 ÷ 0.8 = 52.08 gallons per hour, or 195.31 liters per hour.
Check the flow at your fuel pressure
A fuel pump's flow goes down as pressure goes up, so compare the result with the pump's flow chart at the pressure your system runs. Summit Racing puts carburetors between 4 and 7.5 psi and fuel injection usually between 35 and 65 psi. A pump that flows plenty at carburetor pressure can come up short on an EFI system.
Fuel flow by horsepower
Gallons per hour at peak power, before any margin, for each of the calculator's BSFC values:
| Horsepower | Gasoline (0.5) | Boosted gasoline or E85 (0.7) | Boosted E85 (0.9) | Methanol (1.0) |
|---|---|---|---|---|
| 300 | 25.00 | 35.00 | 45.00 | 50.00 |
| 400 | 33.33 | 46.67 | 60.00 | 66.67 |
| 500 | 41.67 | 58.33 | 75.00 | 83.33 |
| 600 | 50.00 | 70.00 | 90.00 | 100.00 |
| 700 | 58.33 | 81.67 | 105.00 | 116.67 |
| 800 | 66.67 | 93.33 | 120.00 | 133.33 |
| 1,000 | 83.33 | 116.67 | 150.00 | 166.67 |
Calculated with the formula above, using gasoline's weight of 6 pounds per gallon from Summit Racing.
Size the injectors for the same horsepower with the fuel injector size calculator. If you're running a carburetor, the CFM calculator sizes it.
Frequently Asked Questions
How do you calculate fuel pump size?
Multiply peak horsepower by BSFC to get pounds of fuel per hour. Divide by 6 for gallons per hour or by 1.6 for liters per hour.
What size fuel pump do I need for 500 hp?
A naturally aspirated 500 hp gasoline engine at 0.5 BSFC burns about 41.67 gallons per hour at peak power. With a pump sized so the engine uses no more than 80% of its flow, that is 52.08 gallons per hour.
Should I add a safety margin to the fuel pump size?
The calculated flow has no margin, so a pump rated at exactly that number would have nothing in reserve at full throttle. Dividing the result by 0.8 sizes the pump so the engine uses no more than 80% of its flow.
Why does a fuel pump flow less at higher pressure?
A pump's flow drops as the pressure it pushes against rises. Carbureted systems run about 4 to 7.5 psi and fuel injection usually 35 to 65 psi, so check the pump's flow chart at your system's pressure.
Does E85 need a bigger fuel pump?
Yes. E85 has a higher BSFC than gasoline, so the same horsepower burns more fuel. A 500 hp engine at 0.7 BSFC needs about 58.33 gallons per hour, compared with 41.67 on gasoline at 0.5.
