Fuel Injector Size Calculator

Find the injector flow rate your horsepower goal needs, in lb/hr and cc/min, with a fuel pressure correction.

Typical: 0.45–0.50 naturally aspirated, 0.60–0.65 boosted.
80% leaves headroom.
Fuel Pressure (Optional)
The pressure the injector is rated at.
Fractions and decimals both work.
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Lb./Hr. per Injector
Metric flow
Total fuel
Rated size needed
Max HP at 100% duty
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Injector Choices

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BuildHPBSFCLb./Hr.cc/minRemove

How to Size Fuel Injectors

An engine burns a predictable amount of fuel per horsepower per hour, called brake specific fuel consumption (BSFC). Multiply by the horsepower, split it across the injectors, and leave headroom so they don't run wide open.

Injector flow (lb/hr) = HP × BSFC ÷ (injectors × max duty cycle)
cc/min ≈ lb/hr × 10.5   Flow at a new pressure = rated flow × √(new PSI ÷ rated PSI)

Worked Example

Tips

Boosted engines use more fuel per horsepower, so use a higher BSFC. E85 needs roughly 30% to 40% more fuel flow than gasoline for the same power, so size injectors up accordingly. Injectors are rated at a specific pressure (often 43.5 psi / 3 bar); raising fuel pressure raises flow with the square root of the ratio. Round up to the next available size.