HEI & Blaster 2

The HEI has a built in current limit and dwell control. Inquiring people like me place a 0.1 Ohm non-inductive shunt in series, and measure the current using Ohms law and a scope. The current will ramp up, then flat top when limit is reached. Typically current limits are set to 4-7A. Many coils will start to fail at 5A continuous with long term use, but at higher RPM, the average current is less.

Spark energy increases by, current squared, times coil primary inductance.

At higher RPM the charge time is insufficient for single coil systems, so the current limit is often not a consideration above 4000 RPM.

Picture shows current limit of 5.4A. This is from an ignition I made, not HEI, but result would be similar.