Fuel Injector Calculator

LIGUORI DRAG RACING

Size your fuel injectors

Estimate injector flow for your horsepower goal, fuel, and engine combination. Enter power at the crankshaft.

Engine crankshaft power before nitrous Power units Number of injectors Induction type Nitrous system Desired base fuel pressure (PSI)Set with the regulator reference hose disconnected. Boost settings are below.Fuel type Fuel brand Fuel grade Specific gravity (optional)

Selecting a fuel fills its published specific gravity. You can enter your own value. Specific gravity takes priority over the advanced density override.

Maximum duty cycle (%)

Fuel pressure settings

Fuel pressure unitsInjector catalog rating pressure (PSI)Use the pressure at which the injector’s listed flow was measured.Pressure regulationMaximum boost (PSI)Used for turbocharged or supercharged setups. Naturally aspirated calculations use zero boost.

Injector differential pressure = rail pressure minus intake-manifold pressure. With 1:1 regulation, rail pressure rises with boost and injector differential stays at the base setting.

Fuel consumption and density settings

Use measured values when available. Leaving an override blank uses the displayed estimate. A BSFC override is already for your selected fuel; no additional fuel multiplier is applied.

BSFC override (optional) BSFC units Fuel density override (lb/US gal, optional)

Specific gravity is dimensionless. Density conversion uses water ≈ 1 g/mL for sizing estimates, without temperature correction. Use the manufacturer’s stated reference temperature and your current fuel batch information. Clear specific gravity to use the advanced density override.

ESTIMATED MINIMUM CATALOG FLOW PER INJECTOR

— lb/hr

—cc/min per injector at catalog rating pressure

—Fuel through main injectors (US gal/hr)

—Duty cycle used (%)

BSFC means brake specific fuel consumption: fuel mass used for each unit of power. Required actual injector mass flow = crankshaft hp × BSFC ÷ injector count ÷ duty cycle. The displayed catalog rating converts this requirement using √(catalog rating pressure ÷ desired injector differential pressure). Higher differential pressure can increase injector flow, but fuel demand is unchanged. Confirm the injector’s operating-pressure limits and calibration, and verify pump flow at the required rail pressure. Volume flow is calculated from fuel density. Default estimates are starting points and fuel composition varies. Select an injector rated at or above this flow at your actual injector differential pressure. Nitrous fuel mass is added separately using added nitrous power × nitrous BSFC; only dry / EFI delivery is included in main injector size. Wet-system fuel is counted in shared-pump demand when selected. Staged or unequal injectors require a combination-specific calculation.

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