Engine components produced during the '70s smog-era were oftentimes aimed at reducing emissions and typically had an adverse affect on performance, lending to their negative hobbyist perception. That wasn't always the case, however, and it certainly wasn't true at Pontiac. Since tailpipe emissions and fuel economy were great concerns during that time, Pontiac engineers focused on improving production consistency by tightening component tolerances and utilizing low-maintenance designs.
Attempting to boost output from their smog-era Pontiac engine, hobbyists oftentimes seek the high-dollar '60s and early '70s performance pieces. Years of research and testing, however, indicate that, from a performance standpoint, little separates the smog-era cylinder head, intake manifold, and M4M Quadrajet castings from their early-year counterparts. In some instances, the later units actually contain greater performance potential-a true testament to the efforts of the Pontiac engineering team.
Another smog-era component that's proven itself worthy in myriad applications is the High Energy Ignition (HEI) system. HEI is a totally self-contained unit that offers as much as 35,000 volts of spark energy with proven reliability, and is an excellent alternative to the high-dollar aftermarket ignition systems many choose for street or moderate race applications. With so many used units available today, an HEI can oftentimes be purchased reasonably from salvage yards or at swap meets, but they aren't always reusable.
Follow along as we explore the critical wear areas and prepare a used HEI for many miles of low-maintenance enjoyment.
Ignition Basics
An ignition system is responsible for igniting the compressed air/fuel mixture within a cylinder. Combustion pressure drives the piston downward in its bore, applying torsional force on the crankshaft, also compressing the mixture in an adjacent cylinder. Since complete combustion requires a fixed amount of time, the distributor physically alters the initial combustion point, depending on engine load and/or piston speed. Referred to as "spark advance," it's measured in degrees of crankshaft rotation and uses piston travel towards and away from Top Dead Center (TDC) as its reference point.
The breaker points within a conventional distributor are what transfer electrical current from the coil to the spark plug. A magnetic field builds within the coil while the points are closed, and the duration that the points remain closed is referred to as dwell angle. When the points open and the magnetic field collapses, the result is an intense electrical spark that travels the air gap from the spark plug's electrode to its ground strap, effectively igniting the compressed mixture.
The High Energy Ignition (HEI)...
The High Energy Ignition (HEI) system was developed by Delco Remy in the early '70s and was designed to improve spark intensity and maintain emissions. Pontiac first used HEI on specific applications in 1974, and then on all of its V-8 engines from 1975 forward. Vintage Delco literature states that its large 135mm-diameter cap was required to prevent cross-arcing from the increased spark intensity.
Pontiac's predecessor to HEI...
Pontiac's predecessor to HEI was the Unitized Ignition system. Similar to the Transistorized Ignition of the '60s, conventional breaker points gave way to an electronic triggering system. Unitized didn't, however, require a ballast resistor to lower operating voltage or remote-mounted coil.
An HEI's electronic module...
An HEI's electronic module eliminates the need for breaker points. Triggered by magnetic pulse, it controls dwell time more consistently and improves coil saturation at all engine speeds. Since the module has no moving parts (as noted in this cut-open one), it requires no periodic maintenance, and replacement is only necessary if its internal electronics fail. A daub of heat-sink compound between it and its mounting surface helps dissipate the heat it generates.
Dwell angle changes as the breaker points wear, and as dwell exceeds its specified range, spark intensity degrades (and spark advance changes), subsequently affecting emissions and performance. Periodic breaker point adjustments and eventual replacement are required to maintain peak performance and minimal emissions. While such maintenance may seem minute today considering how little our Pontiacs are driven, it was, however, a major concern for manufacturers when forced with long-term emissions compliancy back in the '70s.