Around 1975, General Motors made a significant advancement in stock passenger ignition technology: the High Energy Ignition (HEI). One of its major features was installation simplicity. The coil was contained within the distributor cap and it required connection of only one 12-volt wire. Significantly better than the standard at the time, the points distributor and the HEI went on just about everything GM produced until the mid-'80s, when electronics began running the engine controls. This ignition was designed for low-revving street vehicles.
Racers running a stock HEI often develop a high engine-speed miss around 5,500 rpm that essentially acts as a rev limiter. The HEI can't develop enough ignition energy to properly fire the spark plugs beyond that rpm.
Because the stock HEI was never designed for racing, better and more dependable racing ignition systems have been developed. You won't find an HEI on a race car in the higher divisions, but many Street Stock and other entry-level racers are required to run OEM-type ignitions. Because the majority of this population races the Chevrolet 350, they're faced with competing using the bone-stock HEI.
The good news is that there are options available for hopping up an HEI. Depending on your rules, options could be anything from simply locking out the advance to using the HEI to trigger a full-blown, high energy external ignition control capable of running a V-8 up to 14,000 rpm.
"Stock" Tactics The first option is to purchase a new HEI and perform a few basic modifications to maximize its capabilities. Because energy is required for a spark to jump an air gap, minimize your plug gaps. Start with a gap between .032 and .035 inch, which should be a good amount to make a spark and give the fuel/air mixture enough space to get in there and light up. While you're at it, install a new set of spiral core wires designed for racing.
With that done, block off the vacuum advance. It isn't necessary for racing applications because the engine normally operates at an rpm range-even during cautions- too high for it to work. Do the same with the mechanical-advance mechanism under the cap. It is possible to find an advantage with a properly tuned, dependable mechanical advance, but those are rarely found stock because they're prone to sticking over time when the hinge points on the throws become worn or the springs break.
The springs are often so weak they go to full advance too early. One stable solution is to lock it up (you can tack-weld the weights in the closed position), set your engine's advance for the racing rpm range, and forget about it. Most ignition manufacturers offer an inexpensive device to lock out the vacuum advance, and some even offer a mechanical advance lockout.
"Modified" Stock These steps are normally allowable even under the most restrictive rules. How far to go beyond this is up to you, your wallet, and your tech inspector. As with everything else on the race car, different inspectors have different parameters, even when the rules stipulate "stock." You might want to do a little asking around to see exactly what is legal and how much you can get away with.
If you want to continue down the HEI improvement path, look at tuning your own advance curves. Ask your engine builder when he recommends your engine be at full advance. You can order more durable mechanical-advance kits that come with several springs in different weights, and with a little experimentation and a lot of patience, you can tune your mechanical advance to your needs. This is helpful because, while locking the engine at full advance is a viable option, it can also make it difficult to restart when it's hot and also cause the engine to bog when accelerating from lower rpm (read, when coming out of the turns).
"Outlaw" Stock For even more performance, start replacing some of the key components. The drawback of stock HEI systems is that at higher rpm (usually beyond 5,500), there isn't enough dwell to properly charge the coil. Dwell is the amount of time the coil is allowed to recharge between firings, and it's affected by the number of cylinders and the rpm. On an eight-cylinder motor, theoretically, dwell at 5,000 rpm is just .0015 second. If you are pushing 7,500 rpm on the racetrack, the coil has just .001 second between firings to recharge.
An HEI is an inductive system, meaning the ignition coil is the sole source of energy storage until the energy is released to fire the spark plug. Ignition systems using a separate spark box are usually capacitive-discharge systems, which use a storage capacitor to hold energy. The capacitor releases the energy to the coil, which ups the voltage and sends the energy to the spark plug.
One of the easiest ways to significantly improve the performance of your HEI is to replace the stock coil with one designed for more performance. Again, almost every ignition manufacturer has its own version. A performance coil features updated materials and windings that offer less resistance to the electrical charge. This means the coil charges faster and transfers more energy to the spark plugs. More energy at the spark plugs also means you can open up the spark plug gap. When the gap is larger, but not too large, you typically get a more efficient burn in the combustion chamber.
The ignition module in an HEI is also easily upgradeable for horsepower gains. Think of it as the ignition's brain. It controls the current sent to the coil, which, if fed a higher current, can feed the spark plugs at increasingly higher rpm. The module also electronically increases the duration of the spark (dwell), and, in some brands, can be used as a rev limiter. Like the coil, racing modules are made by most ignition manufacturers, but use the four-pin plug format almost exclusively. Keep this in mind when searching for your donor HEI. Of course, if you have gone this far, you might as well invest in a complete HEI upgrade kit, which normally includes the coil and module as well as a new rotor and cap. If your tech inspector is on top of it, an ignition cap that doesn't look stock is easy to spot. There are also options to add an external, high-intensity coil to the system that mounts to the firewall. These are powerful and run cooler because they can be mounted farther away from the engine, but are expressly forbidden in many series.
Full Race
The next step is to go with a complete HEI-type distributor designed exclusively for racing.
An advantage of a racing-specific HEI is that the advance curve can be better tailored to fit the needs of a racing engine. Most street motors need the spark fully advanced fairly quickly in the rpm range, but the typical race engine needs the advance curve coming in higher up the rpm range. There are units with their own mechanical-advance assembly to eliminate premature wear and sloppiness from the stock advance. When ordering a part like this, have the following engine information available: compression ratio, displacement, induction system (carburetor size and type), transmission (automatic or manual) duration and lift of camshaft, octane rating of fuel, normal racing rpm range, and the total weight of your race car.
If your tech man doesn't care what kind of HEI system you run, some companies, such as MSD, produce a high-end full-race HEI-type ignition complete with a billet-shaft housing. A billet housing does allow the shaft to be contained to tighter tolerance than stock so it spins true at very high rpm and allows the use of bearings in areas where bushings are normally used to support the distributor shaft.
Finally, you can go the full monty and completely upgrade the ignition from an inductive-discharge system to a capacitive ignition system triggered by the HEI. Remember, a capacitive system does not use the coil to both build the electric charge and store it. Instead, a separate capacitor stores a lot of electrical energy (think of it as a gas tank) and releases a portion of it to the coil to fire a cylinder.
The coil, in turn, boosts the charge and sends it on its way to the spark plug. You can use one or two capacitors constantly charging while the coil and module route the energy to the correct cylinders. The plus side is that these systems are capable of firing all eight cylinders of a stock car race engine with a good hot spark to 14,000 rpm.
Unfortunately, systems that convert an HEI from inductive to capacitive discharge require several external components, so disguising it is nearly impossible. These are best suited for situations where an HEI is not specifically required by the rules.
HEI Distributor Myths
Companies specializing in these ignitions deal daily with educating racers about how to overcome the drawbacks of the stock HEI. They also have to deal with quite a few misconceptions.
Myth 1: Inductive ignitions, like HEI, are not as good for racing as CD (capacitive discharge) ignitions.
It depends upon the application. Today, high output HEI modules and coils that saturate fast enough to fire consistently at high rpm are being made. This also allows possible wider spark-plug gaps. A benefit of wider plug gaps may be a more complete burn of the fuel mixture.
Myth 2: Internal coils (in the cap) overheat.
HEI coils can run cooler because they are encapsulated in epoxy, which dissipates heat more efficiently than oil-filled coils. The solid epoxy, in comparison to oil-filled coils, also eliminates the possibility of leaks.
Myth 3: Ignition coils last forever.
For peak operation change the coil each season. They can lose efficiency so a new one should be installed. You should also do the same with spark plug wires.
Myth 4: Lock the advance and race.
A fully locked advance usually leads to hard starts. Your motor may run better with less-than-total advance at some rpm. The upside of a locked advance is that you don't have weights and springs wearing and potentially failing.
Myth 5: You have to run an alternator with an HEI system.
Any electronic ignition system, whether it be capacitive discharge (CD) or inductive (HEI), will run optimally with an alternator. The more input voltage you put into an ignition, the more output you get out of it. Some HEI systems only draw 2 to 3 amps off the battery. CD systems draw between 6 and 14 amps off the battery. An alternator will keep the battery and the ignition at their optimum for the entire race. Remember, an alternator draws less than 1 hp (another myth is that alternators rob too much horsepower).
Myth 6: Because this is a race car, use solid-core plug wires.
HEI systems run better with spiral-core plug wires. The spiral core prevents internal-wire vibration and electronic interference.
Myth 7: The dielectric grease you place under an HEI module insulates the heat.
No. In fact, the grease transfers the heat produced by the module to the distributor housing. The HEI housing becomes a heat sink.
Myth 8: You must phase the rotor on an HEI.
On an HEI, if you install your vacuum advance eliminator using the holes in the housing that were originally for the vacuum advance, there is no cause for rotor phasing. It will already be phased correctly due to the original design.
