To Ballast or not to Ballast?

Depending upon the primary winding resistance, the coil may or may not need a ballast resistor. If you're using the coil that is matched with a Mopar ECU and ballast resistor, you will overheat the coil if you run the coil for more than a few minutes without a ballast resistor using a Mopar ECU.

Coils (like the e-core) that don't require ballast resistors have low primary coil resistance (HEI e-core coils have 0.5 ohms) and are designed for use in CDI ignition systems or variable dwell inductive systems (like HEI). You will burn out a low resistance coil with the fixed dwell Mopar ECU if a ballast resistor is not used.