Pertronix 91247 Ignitor II for Ford 4 Cylinder Engine Adaptive dwell maintains peak energy throughout the entire rpm range, reducing misfires while improving engine performance. Compensates for inherent electronic delay by adjusting the spark timing throughout the entire RPM range. Synchronized peak current and spark timing reduces heat build-up. Senses startup and develops more energy for quicker, easier starting. Built in reverse polarity and over current protection shuts down the system, preventing component damage.