What matters
- Injector flow depends on horsepower, BSFC, injector count, and the chosen duty-cycle ceiling.
- A 600 hp six-cylinder at 0.75 BSFC and 80% duty needs about 93.8 lb/hr per injector.
- Published flow is tied to fuel and differential pressure; the final part choice needs characterization data.
The core sizing equation
Brake-specific fuel consumption is the fuel mass needed per horsepower-hour. It is an assumption, not a universal engine constant. Ethanol blends and conservative rich operation generally require a higher BSFC assumption than an efficient naturally aspirated gasoline engine.
Worked example: 600 hp, six injectors, E85
Use a planning BSFC of 0.75 lb/hp-hr and an 80% maximum duty cycle. The engine has six port injectors.
Flow = 450 ÷ 4.8
Flow = 93.75 lb/hr per injector
This is the calculated minimum at the stated assumptions. It is not a recommendation to buy the nearest nominal size without margin.
Compare the assumptions
At the same 600 hp and 80% duty cycle, a gasoline BSFC assumption of 0.55 produces 68.75 lb/hr. That difference shows why copying an injector recommendation without its fuel and BSFC assumptions is risky. Use crank or wheel horsepower consistently with the BSFC basis and state whether auxiliary or direct injection supplies part of the fuel.
Pressure changes injector flow
Injector flow is characterized at a stated differential pressure. Rail pressure rising one-for-one with manifold pressure maintains the differential; a system that loses differential pressure under boost does not deliver the catalog flow. DeatschWerks’ public fuel calculators likewise ask for BSFC, duty cycle, injector count, fuel, base pressure, and boost because those inputs change the answer.
Sources and methodology
Calculations are shown so the assumptions can be checked. Safety-critical fitment, fueling, and calibration decisions must be verified against current manufacturer documentation and the professional responsible for the work.