The Powerfire I represents the latest state-of-the-art design in modern ignitions systems. It's most outstanding feature is it has an external knob that allows timing adjustment while the engine is running. Each click of the knob advances or retards the timing 1/2 degree. This distributor can be used with the Powerjection systems but the spark control feature of the Powerjection cannot be enabled. Works for 351W Small Block Ford.