Dispelling Confusion and Debunking Myths


When it comes to reliable and easy to use ignition systems, the HEI distributor is the one at the top of the list. A single 12-volt wire is enough to operate, and it can be easily stabbed into any distributor-fed Chevrolet engine. It’s a must have for hot rodders. GM’s HEI distributor was envisioned and ultimately built by the Delco-Remy division of General Motors and found its way into production vehicles beginning in 1974.

These spark igniters worked so well that they were used on all General Motors engines. You can find them in everything from their inception to their phasing out in the mid-1980s. In fact, the HEI is such a well-thought-out design that the folks at Performance Distributors took the concept and improved it – to more than General Motors engines.

When talking about a factory HEI, the module is probably the most misunderstood piece of the puzzle. (Right to left) The four-pin module was used on carbureted engines with traditional vacuum and centrifugal advance. The five-pin module was introduced in 1978. It was an early attempt at electronic ignition timing control. The extra pin is connected to a knock sensor. Seven-pin and eight-pin modules are used on early computer-controlled engines that use fixed-timing distributors.

The HEI distributor consists of a control module and a magnetic sensor inside the housing which replaces the contact points and condenser previously used. The function of the control module is to provide the same ignition pulse as the circuit breaker points previously found in a point and condenser system.

However, early HEI distributors proved to be less reliable in high performance applications and gained a bad reputation. Unfortunately, the units were infamous for not providing a solid spark at engine speeds above 5000 rpm. It didn’t take long for GM to rectify the situation by modifying the modules and coils to deliver increased spark energy at higher engine speeds. When used in OE applications, these changes have proven to be the perfect solution. Unfortunately, enthusiasts are never satisfied with OE applications.

HEI Distributor

Although GM has designated a particular position for the number one plug wire, as long as the firing order is correct, the distributor doesn’t care which “lug” is used as number one.

HEI goes high performance

Today, there are a dizzying array of high-performance modules, coils, and complete off-the-shelf HEI distributors available for performance junkies. These modern versions of a vintage ignition have fueled the market and fueled the combustion of countless engines.

Like many parts and products offered to consumers, there always seems to be untruths and misinformation spreading like wildfire. Added to this is the fact that the Internet offers anyone with an opinion a global venue to say what they believe to be true. Because of that, I thought maybe now would be a good time to clear the fog, so to speak. In fact, if you want to learn a little more about troubleshooting an HEI distributor, click here.

For some solid information you can store in your noggin, we reached out to Steve Davis of Performance Distributors. We wanted his input to debunk some of the most popular rumors and innuendos. With Steve’s help, we’ve compiled the following most common misconceptions about ignition and the truths that need to be told.

Lying: A long standing rumor that is often told relays that an inductive ignition – like an HEI – is not as good for use in high performance engines as a capacitive discharge (CD) ignition.

Truth: “This myth is only true when compared to a stock HEI distributor,” Davis says. “Today we make high output modules and coils that saturate fast enough to fire consistently at high RPM. This firing capability also allows the use of wider spark plug gaps. In fact, we suggest 0.050 to 0.055″ with our DUI distributor. The benefit of a wider spark plug gap is more complete combustion of the fuel mixture.

HEI Distributor

A common misconception is that the HEI coil can get hot, shortening its life since it is covered. This is not true because an HEI coil generates less heat than a traditional oil filled coil.

Lying: Since a HEI distribution coil is mounted in the cap and is covered, can it overheat?

Truth: “That’s probably the oldest myth of any HEI distributor,” jokes Steve. “First of all, HEI coils only draw two to three amps. Compare that to an oil-filled external coil that draws about six amps, and there’s no way it could get that hot when working properly. The lower amperage draw actually results in a much cooler HEI coil. A HEI coil also runs cooler because it is encapsulated in thermal epoxy. This epoxy dissipates heat more efficiently than oil filled coils. Also, a coil filled with oil can leak. Solid epoxy eliminates the possibility of leaks. You can also lose a small amount of spark intensity when running a coil wire to an external oil filled coil. The spark must travel a longer resistance path.

Lying: A billet distributor housing is far superior to a casting.

Truth: “There is no benefit to a billet distributor housing in terms of increased performance – the castings are stable and straight,” according to Steve. “Internally, the bronze bushings used in Performance Distributor’s DUI dispensers are oil impregnated and extremely durable.

Lying: A stock HEI will only do a good job when used in low to mid-range performance applications.

Truth: In reality, the advance curve typically found in a stock HEI distributor is not fully advanced until 4000-4500 rpm, which is very slow. If your engine’s camshaft has a power band that starts at 2500 RPM (or less), your advance curve will not match your camshaft’s power band. This will cause a significant loss of horsepower/torque.

Additionally, low to mid performance engines (and even stock engines) benefit from a more intense spark at idle, throughout the rpm range, as the fuel is burned more completely.

HEI Distributor

Although some believe that using a solid core wire will help provide a better spark, with a HEI unit this is not a good idea. A spiral core wire will help prevent electronic interference.

Lying: Connecting or not connecting a vacuum lead can add or detract from maximum power.

Truth: “Idle advance of a distributor does not result in any power gain or loss,” says Steve. “Engine timing advance, via vacuum advance, immediately begins to decrease as soon as you accelerate. In fact, at wide open throttle, there is no vacuum advance. However, we recommend that you connect your vacuum advance hose to a direct manifold vacuum. This is because it will provide you with more vacuum advance at idle. This can help keep your spark plugs cleaner. Some engines will idle too quickly with the line connected to a manifold vacuum.If this happens, you will need to connect your vacuum cleaner lead to a handheld vacuum.

Lying: The number one plug wire must be located at a specific terminal on the distributor cap for the motor to operate properly.

Truth: As long as your number one cylinder is at top dead center on the compression stroke, it doesn’t matter which terminal you use for your number one spark plug wire. This means that no matter what position you stab the distributor in the engine, as long as you can move the distributor to advance or retard timing as needed, any terminal can be connection number one.

Lying: If you have a high compression engine – or one that produces a lot of horsepower – you should use solid core spark plug wires.

Truth: HEI systems will work best using coiled spark plug wires. The spiral core prevents internal wire vibration and limits electronic interference.

Dielectric grease placed under a module is not there to protect the module from heat. It is used to help the module transfer the heat it develops to the distributor housing.

Lying: The silicone grease that you place under a HEI module is designed to insulate the module from heat.

Truth: It’s not. In fact, the silicone transfers the heat produced by the module to the splitter box. In effect, the HEI package actually becomes a heat sink for the module.

Lying: If you decide to eliminate the vacuum advance module, you must phase the rotor in the distributor.

Truth: According to Steve, “if you install your vacuum advance eliminator using the same holes in the housing that were originally used for mounting the vacuum advance, there is no cause for phasing of the rotor.It will already be phased correctly due to the original design.

These myths and untruths have been perpetuated for decades, and it’s hard to believe that many still believe them. Fortunately, we were able to find out the truth and clarify things, thanks to the performance distributors.


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