Fuel Pump Sizing Calculator
Size a fuel pump (GPH / LPH) for HP target — pressure-compensated with 20-30% safety margin.
How to Use
- Enter HP target, fuel, and system base pressure.
- For turbos, add expected boost (rail pressure rises 1:1 with MAP on returnless).
- Pump is rated at a reference pressure — tool converts to your operating pressure.
Target
Pump spec
Formulas
Fuel demand
ṁ_fuel = HP · BSFC (lb/hr)
GPH
GPH = ṁ_fuel / ρ
Pressure correction
GPH_at_P = GPH_rated · √(P_rated / P_actual)
Operating pressure
P_actual = P_base + boost (returnless 1:1)
Frequently Asked Questions
Why does pump flow drop at higher pressure?
Pump is a constant-displacement device. Back-pressure steals shaft power; flow drops ~sqrt(P_rated / P_actual).
Returnless vs return?
Return systems run constant pressure — pump runs full tilt. Returnless with PWM matches flow to demand but can struggle at max with base pressure + boost.
Safety margin?
20% is a minimum. 30-40% gives headroom for rail pressure spikes and hot fuel cavitation.
Common Use Cases
In-tank swap
Decide between 340, 450, 525, DW65c.
Twin pump staging
Check if a single covers target HP or if a second must stage in.
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