High energy ignition
High energy ignition, also known as H.E.I., is an electronic ignition system designed by the Delco-Remy Division of General Motors, and introduced on some GM vehicles in 1974, including the Camaro Z28 Special High Performance (with 3123 units factory installed)[1] and 1974 Buick Century Gran Sport Stage 1 (distributor code 1112521). It was used on all engines from 1975 through the mid-1980s. There were many design variations over the years, and provisions for computer controls were added for some applications starting in the late 1970s. A predecessor system was optional on Pontiacs as "code 704 UPC K65 unitized ignition system" for the 1972 and 1973 model years.
HEI is characterized by the incorporation of the ignition coil into the distributor cap for most applications. The system consists of a control module and a magnetic pickup mounted in the distributor. This eliminates ignition points and the coil wire. The control module performs the same function as the breaker points in a points and condenser system.
Control modules
There are four basic types of HEI control modules: four-, five-, seven-, and eight-pin. The four-pin module was used on carbureted engines and uses conventional mechanical timing controls (vacuum and centrifugal advance mechanisms). The five-pin module was introduced in 1978 and was an early attempt at electronic timing control; it contains a provision for connecting a knock sensor. The seven- and eight-pin modules are used on early computer-controlled engines. The seven- and eight-pin modules contain no mechanical timing control mechanisms as the computer controls ignition timing. Late 1980s GM cars and trucks used a slim distributor cap HEI with a separate ignition coil on throttle body (TBI), PFI, and SFI injection equipped engines. These distributors were not stand-alone units because they did not contain mechanical timing controls.
Upgrading
HEI distributors are a popular swap on older GM cars originally equipped with points and condenser type ignition systems. The HEI system produces a more powerful spark, which allows for a wider spark plug gap for surer ignition of a fuel/air mix that may not be optimal. The HEI setup has also become a popular swap into non-GM vehicles.