HEI Distributor Swap, Facts You May Not Know!

High Energy Ignition, also known as H.E.I., is an electronic ignition system designed by Delco-Remy, a division of General Motors. It was introduced in limited numbers in 1974 and was used on all GM vehicles from 1975 through the mid-1980s. Most HEI systems have the ignition coil mounted in the distributor cap. Instead of breaker points and condenser, a control module, and magnetic pickup are mounted at the distributor base.

The HEI system produces a more powerful spark, which allows for a wider spark plug gap and better ignition of the air/fuel mixture. The control module is more reliable and is maintenance-free. Four types of HEI modules are used: four-pin, five-pin, seven-pin, and eight-pin units. The four-pin module was used on carbureted engines with mechanical timing controls and a vacuum advance. A five-pin module was introduced in 1978, enabling the use of a knock sensor and electronic timing control. The seven and eight-pin were used with fixed-timing distributors and computer-controlled engines. Not only have HEI distributors become very popular upgrades on older GM engines equipped with point distributors, but they have also become popular on non-GM engines.

If you are swapping out your point-type distributor for an HEI-type, you must pay close attention to your wiring setup. A new wire circuit must be added to provide sufficient voltage and current to meet the designed performance.

In most cases, if your vehicle is a 1974 or earlier, there are two wires supplying voltage to the positive terminal of the coil: one wire supplies 12 volts from the starter solenoid during cranking, and the other is a resistor wire from the ignition switch, which lowers the voltage to the coil to 7 to 9 volts while the engine is running. If these 14-gauge wires are connected to the HEI distributor's battery terminal “BAT,” There will not be enough current to operate the HEI efficiently, especially at higher RPMs.

A new electrical circuit must be created to eliminate the resistor wire and ensure the coil receives a solid 12 volts. Much science can happen here, but we will keep things simple. An HEI system draws around 4 amps, +/- running. It can surge 20 or more amps during cranking. A minimum of 12-gauge copper wire must be used in the coil feed; if you have an extended length of wire, a 10-gauge wire may be appropriate. We will also incorporate a 30-amp relay and a 20-amp fuse. The relay will take the increased amperage load off the ignition switch and original wiring, while the fuse will protect the circuit. The diagram below shows the suggested wiring. Always refer to the manufacturer's recommendations before modifying or wiring any part or component.

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