What is inside an HEI distributor?
GM introduced its trademarked High Energy Ignition system (HEI) in 1971 as an upgrade over points-style, divorced coil distributors. The term has become generalized to include any distributor of the type.DescriptionLike any distributor, the HEI can be thought of as a spinning on/off switch for the spark plugs. As the rotor (the spinning part inside that carries electricity) hits the spark plug wire contacts, it closes the circuit from the coil to the spark plugs.CoilThe main thing that distinguishes an HEI from older distributors is that HEIs use ignition coils mounted directly on the distributor cap. This reduces voltage drop between the coil and distributor, making for a hotter spark.ModuleBased on aftermarket retrofit units first engineered by Pertronix, HEIs use a magnetic sensor and miniature computer (module) to sense rotor position and alter spark duration.Advance LeversIn order to advance or retard ignition timing on demand, HEIs use a cantilever system where the rotor connects
