Standard Motor Products developed these High Flow fuel injectors for increased performance on all Electronic Fuel Injection (EFI) equipped Harley models. These High Flow injectors are highly recommended when you have an "Opened-Up" muffler, Performance Exhaust System, or Low Restriction Air Filter installed. Work great when combined with our ZPN721325 Variable Fuel Pressure Fuel Regulator. This High Flow fuel injector is very easy to fit as it plugs in like the stock injector. Are sold each, always install in pairs.