Ballast, Blaster II, ohms, current, friggin volts!

The GM HEI modules have an analog dwell control. It is a form of prediction to set the dwell period based on the the frequency of ignition pulses. It works with resistors and capacitors, comparators and other circuity. It also tweeks for extended dwell at lower RPM. It may also have a current limit. It is a late 70's technology. The IC that Motorola made for these features has been obsoleted for general sales.

The 8 pin module is similar but has hooks to use with a micro control to provide a digital timing reference. It has an input for the the micro to control the ignition driver. When the 8 min module is used without an ECU it is in the limp home mode. It is designed to function on a GM car and defaults to limp home mode for starting, then under ECU control for normal driving. The GM application has a locked distributor ... no mechanical advance. The ECU provides the timing control. If used with mechanical advance distributor and no ECU it works too, and many seem satisfied. Some think adding an ECU to a mechanical advance distributor is the way to go. I think it would be similar to standing in the back of a truck, shooting prairie dogs in a plowed field, while the truck is moving. Or running on top of a train to maintain a certain velocity or position with respect to a ground location. I have never tried any, so do not know for sure.