The formula
injector size (lb/hr) = horsepower × BSFC ÷ (injectors × max duty cycle). BSFC (brake specific fuel consumption) is how many pounds of fuel the engine burns per horsepower per hour. Boosted engines run richer to stay safe, so they need more fuel per horsepower than naturally aspirated ones. Multiply lb/hr by about 10.5 for cc/min.
Why 80% duty cycle
Duty cycle is how much of each engine cycle the injector is open. Near 100%, an injector can't fully close between pulses and fueling gets unpredictable. Sizing for about 80% leaves room for a hot day or the next mod.
E85 needs bigger injectors
E85 has less energy per gallon, so the engine needs roughly 30–40% more of it for the same power. On most E85 conversions, the injectors and fuel pump run out before anything else does.
Fuel pressure changes flow
Injector flow is rated at a specific pressure, often 3 bar (43.5 psi). Flow goes up with the square root of pressure, so raising pressure from 43.5 to 58 psi gives about 15% more flow. Fuel pumps and regulators have limits too, so don't lean on pressure alone.