Upgrade Your HEI Module To Include Rev-Limiting Capabilities

Since its introduction in 1974, General Motors’ High Energy Ignition (HEI) distributor was a major part of cars delivered to consumers until the mid-1980s. This all-in-one ignition was not what some might call compact, but the HEI distributor does incorporate the ignition control module as well as the coil as part of the distributor. The unit is a self-contained, modular-type system that has been a favorite of enthusiasts for many many years.

HEI units became very popular among enthusiasts when hot rodders discovered these self-contained ignition systems could easily replace their factory distributors that utilized breaker points and condensers. The swap to an HEI distributor produced a much-needed, higher output spark for those looking to get the best performance possible from the ignition. This higher energy spark allowed the end-user to institute a wider spark plug gap, which in turn, would help create a more efficient ignition of the air/fuel mixture in the combustion chamber. Even non-GM enthusiasts were quick to notice these benefits, and the HEI setup eventually became a popular swap in other makes as well. I know that might sound strange, and although the HEI was initially a General Motors ignition, many fans of Mopar and Ford realized this as a great upgrade, and Performance Distributors stepped up to the plate to deliver non-GM HEI-style distributors.

HEI module

The Rev Limiting Module from Performance Distributors is a direct fit into any HEI distributor.

It was no surprise that a performance upgrade like the addition of an HEI ignition would find its way into many cars. However, in stock form, this self-contained ignition did have a few limitations. The early HEI module design was limited by slow-acting electrical fields. This caused the HEI to develop spark drop-off at higher engine RPM (usually around 5,000-plus). Performance Distributors went to work and solved the shortcomings of high-RPM spark delivery in HEI units, turning these distributors into an even better enthusiast favorite. But what else makes the Performance Distributors HEI better than the OE offerings?

One improvement is the availability of an RPM-limiting module. The Performance Distributors’ Rev Limiting Module offers high-dwell operation and provides outstanding performance, just like the company’s standard four-pin Dyna-Module. The kicker is, this HEI module incorporates a way for the user to limit engine RPM. The RPM-limiting feature is adjustable via easy-to-use DIP-switch settings that allow you to control the engine’s peak RPM in increments of 100, starting at 5,000 to a maximum of 9,500 rpm. This HEI module is available for all HEI distributors and it mounts in the same location as the stock unit by replacing the entire module and wiring harness assembly. It is even compatible with four-, six-, and eight-cylinder HEI distributors.

I wondered how the Performance Distributors’ HEI module differs from OE, and other than the rev-limit capability, what makes it better than stock. “The construction of the Rev Limiting Module is noticeably different from the traditional HEI-style four-pin modules,” says Brian Caruth of Performance Distributors. “It consists of a large, open circuit board to incorporate the rev-limiting feature. There are eight dip switches located on the top of the module to adjust the rev limiting feature.”

HEI Module

Selecting the correct engine configuration is easy with the bottom two DIP switches (4, 6, and 8 cylinder engines).

Brian continues, “The three-wire harness (pigtail) is also a permanent part of the Performance Distributors HEI module, whereas the traditional-style module has a detachable harness. The circuit board also incorporates an aluminum heatsink for heat dissipation. Another important feature that makes this HEI module better than OE is the increased dwell time. As you may already know, dwell is the charge time needed for the coil to produce a spark. With the dwell increased electronically — by two to three degrees of crank rotation — it allows the coil to produce a longer duration spark.”

HEI module

The module is designed to be used on multiple HEI distributors including 4, 6, and 8 cylinder models. All adjustable functions are done via the DIP switches.

Caruth reminded me the simple installation is accomplished easily, which makes this a perfect ignition upgrade for any enthusiast. In less than an hour, you can upgrade your HEI distributor. By adding the Performance Distributors’ Rev Limiting Module to your HEI, you can also eliminate that large box-style RPM limiter that you probably have mounted on your fenderwell or firewall.

I also know that not every enthusiast is enamored with racing, so is the Rev Limiting Module something the average enthusiast should consider? “The average enthusiast can think of the Rev Limiting Module as an insurance policy to prevent an accidental over-rev, making sure your investment stays in one piece if it should happen,” affirms Brian. “Also, the increased dwell that is built into the module will improve throttle response and low-end performance over a stock HEI module.”

HEI Module

If all switches are positioned to the left, that is for an eight-cylinder engine with a limit of 5,000 rpm. To instigate an RPM limit of 6,500, simply flip the needed switches to equal 6,500 rpm (5,000 + 1,000 + 400 + 100 = 6,500).

I also asked Brian what he would say to an enthusiast who is not sure if purchasing this module is right for them. “This HEI module has all pros and no cons. You will get the performance benefits of more electronic dwell over the stock unit, plus the peace of mind that this module protects the engine from spinning at too many RPM. Throw in the adjustability of the module via the built-in DIP switches, and the RPM limit can be easily changed if engine mods are made that will increase RPM capability.”

Whether you’re running a point-style ignition or have an OE HEI distributor, your hot rod could be better served by taking a look at the offerings from Performance Distributors and realizing how much better your high-performance or even your classic cruiser will perform with this simple upgrade.

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About the author

Randy Bolig

Randy Bolig has been working on cars and has been involved in the hobby ever since he bought his first car when he was only 14 years old. His passion for performance got him noticed by many locals, and he began helping them modify their vehicles.
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