A fuel injector adapter for providing nitrous oxide to an internal combustion engine is disclosed. The nozzle has a central fuel injector passage that terminates at a first outlet end. Fuel from a fuel injector may be passed through the central fuel injector passage. The nozzle also has an inner annular passage arranged circumferentially around the central fuel injector passage. The inner annular passage terminates at a second outlet end. The nozzle also has an outer annular passage arranged circumferentially around the inner annular passage that terminates at a third outlet end. One or both of the inner and outer annular passages is adapted to pass nitrous oxide through it. The nozzle is adapted to fit between a fuel injector and an engine without substantial modification to the engine.