Fuel Injector Size from Horsepower, BSFC, and Duty Cycle
The first spec of any engine build or boost upgrade, which the displacement and horsepower tiles never give: each injector must flow lb/h = HP x BSFC / (n_cyl x duty). A 400 hp V8 at BSFC 0.50 and 80% duty needs 31.3 lb/h (328 cc/min) per injector; add boost (BSFC 0.60) and it jumps to 37.5 lb/h - a 20% bigger injector for the same power, why a boosted build steps up injector size before adding power. Port injection, entered BSFC; not rail pressure or DI. A tuning aid; the measured fueling and the tuner govern.
Formula and source
total_lbh = HP x BSFC; inj_lbh = total_lbh / (n_cyl x duty); inj_ccmin = inj_lbh x 10.5.
The fuel-injector-sizing relation lb/h = HP x BSFC / (n_cyl x duty), with the BSFC ranges, the customary 80% duty cycle, and the gasoline cc/min conversion, a standard tuning-reference result, by name.
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