HEI Distributor Tune-Up

Rather than spend $150 or more on a trick aftermarket distributor, you can build your own high-perf HEI for a lot less that will perform just as well.

Rather than spend $150 or more on a trick aftermarket distributor, you can build your own high-perf HEI for a lot less that will perform just as well.

If there is a standard in the world for a stand-alone electronic ignition distributor for GM engines, it has to be the High Energy Ignition or HEI. This large-cap distributor first appeared on small-block Chevy engines in the middle of 1974 and remained well through the '90s in various other forms. The advantage of the HEI is its longer ignition coil dwell time that can deliver greater ignition current to the spark plugs at high rpm. Add to this its integrated ignition coil in the distributor cap, and the HEI is the go-to distributor for basic GM street engines and an easy replacement for buggy-whip-era points distributors.

We will concentrate on the early four-pin-style distributor and a few of the performance parts that can transform an old sparker into an electrifying ignition system. For the budget car crafter, the trick is to start with a good used HEI. When evaluating old HEI distributors, the first place to look is under the rotor. A common HEI malady is for stray voltage to burn through the rotor and to ground through the small mechanical advance weight pivots. The evidence is a rusty-looking iron oxide film on the inside of the rotor and distributor cap. This is clear indication that the posts will be badly worn. This is often followed with a frozen mechanical advance mechanism. If you find a distributor like this, its best to just keep looking for one in better condition.

Several companies offer HEI mechanical advance kits that offer different springs and weights that can alter the advance curve. In this Performance Distributor, note the position of the slot (arrow). The length of the slot determines the total travel allowed by the mechanical advance mechanism. This distance determines the total amount of timing advance created by the mechanical advance system.

Several companies offer HEI mechanical advance kits that offer different springs and weigh

The best rebuild procedure is to completely disassemble the distributor by unbolting the vacuum advance, module, removing the drift pin and gear and yanking the shaft. This way, the distributor body can be thoroughly cleaned, lubed, and reassembled. Mr Gasket sells an inexpensive distributor shim kit that you can use to reduce the overall endplay down to around 0.015 inch. Most stock HEI's have as much as 0.060 inch or more endplay. The excess clearance allows the drive gear to climb the cam gear and retard the ignition timing. Reducing the endplay eliminates this problem. When buying replacement parts, choose a distributor cap with brass inserts. Less expensive caps use aluminum spark plug wire connectors that corrode and increase resistance. This greater resistance is often the cause of cross-sparking inside the distributor cap. Lube the shaft lightly and then reassemble the mechanical advance mechanism. Another way to eliminate those stray HEI sparks from finding a ground path is to use the plastic rotor screws from Performance Distributors. Finally, always connect any HEI to a switched 12-volt source that does not use a resistance circuit. This will allow it to operate at its maximum potential. One way to do this is by using a high-quality relay to offer switched power to the distributor. With these tricks and a few more outlined in the photos, you can build your own high performance HEI distributor without flattening your wallet.

Parts List

This photo of a four-pin module highlights the connections. Pins W and G as marked on the module (left) are wired to the distributor pickup. These are the triggers that tell the module when to fire the coil. Pin B is tied into switched battery power and is also wired to the positive side of the coil. Pin C is wired to the negative side of the coil and can be used as a tach signal. This wiring layout can be used with any HEI module for any electronic signal distributor (Ford or Chrysler, or whatever) to convert to an inexpensive yet reliable electronic ignition. Just mount the module to an engine-grounded metal frame and you’re ready to rock.

This photo of a four-pin module highlights the connections. Pins W and G as marked on the