Ignition Upgrade

When it comes time to choose a way to fire the fuel mixture of your truck’s engine, options abound. Factory and aftermarket ignition manufacturers offer a variety of systems that may range from a set of points to an electronic billet distributor accompanied by an exotic ignition control that includes rev limits and timing adjustments. Both work fine in their place. In the end, though, the choice comes down to two things: what your application calls for and your budget.

Since the majority of us suffer budget constraints, let’s consider matching your specs with what you need. If you’ve built a mild mill primarily to power you around to cruises and shows, you obviously don’t need a double-throw-down mega-volt ignition control. Most cruisers will benefit from the aftermarket’s offerings of multiple-spark ignitions and improved-output coils, but that also means having to mount an external box with more wiring (though classic trucks generally have plenty of room for such amenities). One system that is commonly used is the GM HEI distributor.

The HEI distributor is a favorite among truck enthusiasts due to its simplicity. The HEI is a complete ignition system in one package; all you need to do is route a 12-volt source wire to the cap, and it’s ready to go! The distributor features a maintenance-free electronic trigger source and an ignition module, and the coil is built in to the top of the cap so there is nothing external to mount or wire, keeping your engine compartment clean and neat.

However, the HEI does have some drawbacks. First, the cap of an HEI has a very large diameter (more than 6 inches at its widest point), which some applications just will not accept without firewall modifications. Also, the factory module and coil are not known for incredible output energy, especially at middle to higher rpm, since GM built the original distributors for a variety of mostly low-rpm daily drivers.

We wanted to take advantage of the HEI’s integral design on a truck that offers plenty of room to handle the large-diameter cap. To stay within our budget, we decided to rebuild one ourselves using new power parts from MSD Ignition, along with a cap, rotor, and dustcover. While many aftermarket companies offer improved-performance HEI modules, MSD started from scratch and developed an entirely new module and housing to meet the company’s output demands. Though ours isn’t going to be a race engine, the high-energy spark of the MSD module will help maintain a smooth idle and will fire the fuel with ease at the occasional romp of the pedal.

Even though the new module is physically larger than the stock one, it still fits neatly within the cap. MSD recommends using only its HEI coil due to its match with the control features and inductance of the module. Together, this combination puts out a powerful spark even through higher rpm where the stock parts compromise. The rebuild will be topped off with a bright-red cap that features brass terminals for improved spark distribution.

We found our rebuild candidate at a local swap meet. It was pretty crusty, but the gear didn’t show much wear, and there didn’t seem to be an excessive amount of endplay in the shaft. Those are definitely items that should be considered and checked. Timing accuracy and the performance of the engine will be affected if the shaft is wobbly. Also, we discovered a newer, albeit used, set of weights upon disassembling the distributor. This could be a catch-22 if the advance doesn’t fit our engine’s needs, but we’ll cross that bridge when the truck is running (We could even drop the distributor at a tune-up shop where it could be spun up and the curve noted or tweaked.) Also, replacement weight sets can be purchased from several ignition companies such as ACCEL or Moroso.

Though this could hardly be called a blueprinted rebuild, our application (or wallet) doesn’t really call for one. This update was easy, and the distributor will be ready to drop into the engine when the refurbishing is completed. Once installed, all we’ll need to do is route a switched 12-volt source wire to the terminal on the cap, and we’ll be cruising down to boulevard!