Introduced more than three decades ago, GM's HEI ignition system has capably powered tens of thousands of vehicles over the years. The setup has remained popular with performance enthusiasts to this day, primarily due to its simplicity. The unitized design, with the coil located in the distributor cap and one 12-volt wire hookup, is hard to beat for ease of installation. There's no question that early, stock distributors come up a bit lacking for high-performance applications, as they have difficultly delivering full spark as rpm climbs, especially above 4,500 rpm. Aftermarket, high-performance HEI units do a much better job; MSD's unit promises full spark up to 9,000 rpm, which should be good enough for just about any hi-po application. On the other hand, MSD offers a number of options for increasing HEI performance, one of them being the Super HEI Kit, which we installed in a nitrous-huffing '69 Nova.
Running through a brief refresher course, it's important to note that an HEI setup replaces the traditional points and condenser setup with a control module. This module is able to deliver much more spark energy to the plugs than points-and it also allows for greater dwell times, which enable the coil to more fully saturate, or charge, before releasing its energy. And although this setup provides a much hotter spark to the plugs than with points, it still has a basic limitation. Even the best HEI systems are inductive discharge systems, which means that there is always some dwell time required to fully charge the coil before it discharges. At high rpm, there's less dwell time available, so the coil discharges at less than maximum energy, which can result in a loss of power, and possibly even top-end miss. At the very least, with a less than full-strength spark, the engine can't reach its full power potential. Truth be told, it's the nature of the beast with even the best HEI systems.
That's where the Super HEI Kit comes into play. By incorporating a MSD 6AL box with a Blaster 2 coil in place of the HEI control module and internal coil, the system is converted from an inductive ignition to a high-powered capacitive discharge setup. In short, a CD ignition uses a quickly charged, high-voltage capacitor that stores full energy until the ignition is triggered, sending all the power to the coil, even at high rpm. Each spark gets full juice, regardless of rpm. On top of that, the conversion to an MSD CD ignition system also provides the benefit of multiple sparks for each firing of a plug below 3,000 rpm. Above this level, there's not enough time for multiple sparks, but the system continues to deliver a single, full-power spark.
So when should you consider this type of upgrade? In most applications, a good, high-performance HEI setup, including an aftermarket module and coil, will probably get the job done. And our man at MSD, Todd Ryden, admits that the Super HEI Kit isn't going to add an instant 20 hp. "It will," he told us, "support power gains better and ties in to other modifications, like heads, a cam, or even a carb. It provides some extra oomph." Extra oomph is exactly what we were looking for from our test subject for this install, Pete Cervantes' '69 Nova. Cervantes' ride was already a 11.8 performer when we got a hold of it; after our Mar. '08 "Wake Up 'Stick" cam swap, he's running 11.3 on a 150 shot of juice and making peak power in the mid-6,000-rpm range. With higher rpm levels and increased cylinder pressure, the Nova was the perfect candidate for some extra heat in the ignition department.