PerTronix 91847A Ignitor II Adaptive Dwell Control for Bosch 009 & 050 Aftermarket Distributor 4 cyl Adaptive dwell maintains peak energy throughout the entire RPM range, reducing misfires while improving engine performance Develops on average 4 times more available energy between 3000 and 5000 RPM, and 2 times more available plug voltage 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