FREE TOOL · FUEL SYSTEM SIZING
Injector duty cycle + sizing
Compute the injector flow rate (cc/min or lb/hr) needed for a target HP at a chosen duty cycle ceiling. Stays out of saturation (<85% IDC) where modern petrol turbo fueling lives.
Why duty cycle matters
Injectors run a saturated solenoid + needle valve. Above ~85% duty cycle the needle stops fully closing between cycles → fueling becomes non-linear → AFR diverges from target. Stage 2/3 builds always size for <80% IDC at peak HP to leave headroom for boost spikes and adaptation drift.
Formula: cc/min per injector = (HP × BSFC × 10.5) / (cylinders × duty). The 10.5 constant converts lb/hr → cc/min (1 lb/hr ≈ 10.5 cc/min for petrol density).