GM’s High energy ignition (HEI), designed and built by the Delco-Remy division of General Motors starting in 1974. These units were used on all engines in 1975 through the mid-1980s, with several different variations over the years. Characterized by the incorporation of the ignition coil built into the distributor cap which eliminated the need for a coil wire.
The system consists of a control module and a magnetic pickup inside the distributor housing which removed the ignition points and condenser. The control module basically performs the same function as the breaker points in a points and condenser system.
Within the General Motors supply system, the choice in HEI system type was important based on the engine that it was used in. Each GM division had its own engine design so a Chevrolet distributor would not fit on an Oldsmobile, Pontiac, Buick, or Cadillac engine or visa-versa.
While the distributors may look alike, the parts inside are not alike especially in terms of the ignition coils and the pickup coils. Ignition coils and pickup coils should be considered a matched set. Look at the color codes on each part and match the codes to each other, and to the vehicle/engine family the distributor will be used in. Failure to use the appropriate color codes may result in poor starting and misfiring at low speed.
The control module type is important as well. The control module is the heart of the HEI system. There were three basic types of HEI control modules. The four-pin control module unit, which was used on non-computer controlled, conventional carbureted engines, used mechanical timing controls (vacuum and centrifugal advance).
As the name implies, there were four-electrical terminals in the four-pin control module. Two-large terminals, one for battery voltage input and the other was the ignition coil grounding terminal. The two smaller terminals were for the pickup coil leads. These modules are the most common and are still favored by many oval track racers and street rodders on non-computer controlled engines.
The five-pin control module was introduced in 1978 and the original version included a provision for connecting a knock sensor. This evolution was an attempt at electronic timing control. There are three different versions of the five-terminal control module. The three different types are not interchangeable.
- HEI/EMR Electonic Module Retard used a wire connected to a switch or to an electronic control package. Under certain conditions, the switch or control package will ground the wire, which triggers the retard feature built into the distributor module.
- HEI/ESC Electronic Spark Control used a knock sensor and an electronic controller. The knock sensor sends a voltage signal to the controller, which sends a voltage signal to the distributor module, activating the retard feature within the module.
- HEI/ESS Electronic Spark Selection used an outboard electronic decoder which receives voltage signals from three sources: a manifold pressure switch, the distributor pickup coil, and an engine temperature switch. The decoder processes the information and provides a voltage signal to the distributor module to adjust the amount of advance/retard.
All the five-terminal control modules are used with distributors having conventional centrifugal and vacuum advance mechanisms.
Next was the seven-pin control module which was used on computer controlled engines. Because the computer controlled the ignition timing, there were no mechanical timing control mechanisms on the distributor. These distributors cannot be used on non-computerized engines. The seven-pin control modules are referred to as HEI/EST (Electronic Spark Timing) distributors. All timing advance was pre-programmed into the computer, using information from an array of engine sensors. Base timing could be adjusted, however.
Chevy distributors have casting numbers and casting dates, which can be useful if you are trying to find out the original application the distributor was used in. The housings are date coded and stamped with casting numbers of their respective engine or vehicle application. The numbers were either stamped into an aluminum ring that was wrapped around the upper part of the distributor shaft housing, had a stamped plate riveted to the housing or was stamped into the housing itself.
Casting # Year Notes
1103200 1976 350ci, Corvette L82, California models
1103203 1976 400ci, Chevelle, Monte Carlo
1103209 1976 262ci, Monza, California models
1103239 1977 305ci
1103244 1977 305ci, California Cars
1103246 1977 350ci, Corvette
1103248 1977 350ci, Corvette, California models
1103252 1977 305ci, high altitude Cars
1103256 1977 350ci, Corvette L-82
1103257 1977 350ci, Corvette L-82 California
1103258 1977 350ci, Corvette L-82 high altitude
1103281 1979 305ci
1103282 1979 305ci, California cars
1103284 1980 350ci, Z-28 Camaro
1103285 1978 350ci, Corvette California
1103286 1978 350ci, Camaro, Nova, high altitude
1103287 1980 350ci, Corvette L-48, Manual transmission
1103291 1978-79 350ci, Corvette L-82
1103337 1978-80 350ci, All
1103353 1978 350ci, All Standard, high altitude
1103368 1979-80 305ci, All
1103370 1979 267ci, Malibu, Monte Carlo, Auto transmission
1103371 1979 267ci, Malibu, Monte Carlo, Auto transmission
1103379 1979 305ci, All
1103382 1980 267ci, Malibu, Monte Carlo
1103383 1980 267ci, Impala
1103384 1980 305ci, All high altitude
1103386 1980 305ci, All California
1103387 1980 267ci, All Except California
1103425 1980 350ci, Corvette L-82