Limiting Engine Revs With An HEI Unit From Performance Distributors

Since its introduction in 1974, the High Energy Ignition (HEI) electronic ignition system has been a major part of cars designed by GM through the 1980s. Compact in design, the HEI system incorporated the ignition coil into the distributor cap. With a control module and magnetic pickup incorporated in the distributor, the unit was a self-contained, modular-type system.

Performance Distributors’ new D.U.I. Rev Limiting Racing Module is a game-changer for dirt track engine protection.

The HEI units became very popular when hot rodders discovered these units could easily replace breaker points and condenser distributors. The HEI swap produced a better spark that allowed for a wider spark plug gap and a more efficient ignition of the air/fuel mixture in the combustion chamber. Non-GM enthusiasts were quick to notice these benefits, and the HEI setup became a popular swap in other makes as well.

It was only natural that a performance upgrade like the HEI ignition would find its way into the stock cars at local dirt tracks. However, early HEI units were hampered by slow-acting electrical fields, causing the HEI units to drop sparks at higher RPM (above 5,000 rpm). Companies like Performance Distributors solved the issues of high-RPM spark delivery in HEI units, turning these distributors into circle track favorites.

Performance Distributors’ D.U.I. racing distributors became a standard in dirt track racing for stock cars requiring a factory-stock-style HEI distributor.

HEI Evolution

We talked with Brian Caruth of Performance Distributors about the company’s latest developments in its line of DUI HEI Racing Distributors. The late ignition-wizard, Kelly Davis, a legendary drag racer, began manufacturing an HEI-style distributor of his own design in the mid-70s. The Davis Unified Ignition (D.U.I.) fixed many of the early GM HEI shortcomings and rapidly became a favorite of circle track racers nationwide.

There are several aftermarket companies that make a version of GM’s HEI distributor, but Performance Distributors have never stopped innovating and evolving its D.U.I. technology. As the new millennium began, D.U.I. distributors came standard with the company’s Dyna module and 50,000-volt coil. These units delivered a solid spark at over 7,000 rpm. “We can provide a dependable spark to over 10,000 rpm now,” says Caruth. “Our distributors are all hand-assembled, right here, and each Ultimate Racing D.U.I. Distributor is calibrated on a distributor machine before it leaves the factory,” he adds.

The calibration of the distributor is the extra step that attracts oval track racers to the D.U.I. HEI distributor. “The ignition module has our higher dwell built into it, but the calibration on the distributor machine guarantees a smooth advance curve that translates into instant throttle response and more power,” Caruth proudly states.      

As part of the natural evolution of the Ultimate Racing D.U.I. Distributor, Performance Distributors have designed their new modules with a rev-limiting feature. “Obviously, as part of the ignition module, the rev-limiting unit and controls are strictly internal,” he explains. By internal, Caruth indicated the module and rev controls were completely under the distributor cap.

Each Ultimate Racing D.U.I. Distributor is calibrated on a distributor machine before it leaves the factory

Features And Benefits

The new D.U.I. Rev Limiting Module is available separately or with the D.U.I. Racing Distributor. “If you want to get the most out of the module, it is best to use it with our racing distributor,” says Caruth. “But, racers can take advantage of the module’s higher dwell and rev-limiting ability as a sole unit.”

Features Of The New D.U.I. Rev Limiting Module:

  • Compatible with 4-, 6-, and 8-cylinder D.U.I. HEI distributors
  • High dwell four-pin Dyna module for performance
  • Internal for discreet rev-limiting capabilities
  • Easy to use dip switch settings
  • Able to limit the engine RPM in increments of 100, from 5,000 to 9,500 rpm.

Simple installation

Caruth reminds us that simple installation is accomplished easily due to “the module mounting in the same location as the stock unit, because the entire module and wiring harness assembly are replaced.”

DUI Rev Limiting Module With The D.U.I. Racing Distributor

As discussed previously, the D.U.I. Chevrolet Racing Distributor is already a favorite of dirt track stock car drivers. Performance Distributor’s literature touts the unit’s performance:

  • Twice the firepower of a Magneto
  • No spark box needed
  • Cures top-end misfires
  • Low-amperage draw
  • Rated up to 10,000 rpm

We’ve covered the D.U.I. high-performance HEI distributor many times in the past, going back to our first coverage of Performance Distributors in 2010. At that time, we talked about its ability to push that much voltage in the ignition system.

We also covered the D.U.I. distributor in a two-part series on the basics of dirt track ignitions with Part One and Part Two. Vintage racing engines’ ability to utilize Performance Distributor’s high-performance units did not escape our purview as we covered them in our Upgrade Vintage Ignitions article.

Last year, we covered Performance Distributor’s unique method of building its distributors by hand in The Distinction Of A Hand-Built Dizzy.

In addition to all the options available with the D.U.I. Racing Distributors, another source of company pride surrounds the fact that every unit is hand-assembled in-house.

The D.U.I. Racing Distributor

Despite our ongoing coverage of the product, it’s worth mentioning the benefits of the D.U.I. Race Distributor again. Years of research and development allow the manufacturer to develop a high-voltage coil, and line of high-dwell modules, along with a mechanical advance system that works well for today’s modern dirt track racing engines. “All of the moving parts are hand-fitted to assure the smoothest advance curve possible,” says Caruth.

Using a Performance Distributor’s D.U.I. racing coil means enough juice to allow the spark plug gaps to be opened to an incredible 0.055-inch with a longer spark duration – courtesy of the increased dwell in the Dyna-Module. Caruth ensures us; “These two components produce a spark so intense, it is unmatched by the stock HEI and other ‘performance’ ignition systems, particularly those using external spark boxes.”

A wider spark plug gap, along with a cleaner, more-efficient burn, helps the spark plugs stay cleaner longer, meaning less maintenance in the garage and less chance for problems at the track. A more efficient burn also means more horsepower, which is something every racer is looking for.

As an added bonus, there are no external ignition boxes or coils needed, because everything is part of the distributor. This keeps things simple, with fewer things to break or go wrong. As for the installation, it is a simple drop-in replacement and one-wire hookup. There is not another performance ignition system that is easier to install.

Racing D.U.I. Distributor Upgrade Options

In addition to the new D.U.I. Rev Limiting Module, Performance Distributors has several other options available for the D.U.I. Racing Distributor. For racers using roller camshafts and needing a bronze gear, there is a distributor gear option for these cams.

An instant-timing knob is also available. This feature allows fine-tuning adjustments without using a timing light. Once the total timing is dialed into the engine, fine-tuning can be accomplished with a simple turn of the knob. The knob is marked and can be locked into position to prevent loss of the adjustment, due to vibration. This option allows for 6-degrees of adjustment.

The Deluxe version offers an adjustable slip collar for distributor adjustment in engines with shaved heads and decked blocks. This version also features the Instant Timing knob mentioned above.

A Supreme version covers everything in the Deluxe version, plus, it includes an Ultra-Poly Composite gear added for use with any camshaft. Lastly, a Stealth version of the distributor, which has all the racing goodies inside, but is stock appearing. There are no decals and no polished housing, just a black cap with stock coil cover for a factory look.

Other Advantages

There are additional advantages that are standard in Performance Distributors’ D.U.I. distributors that racers can take advantage of at no additional cost. These include a no-resistance rotor bushing that ensures all of the spark energy from the coil is distributed by the rotor to each contact in the distributor cap. The unit incorporates nylon screws in the rotor to prevent misfires at high RPM.

The D.U.I. Racing Coil is designed to run cooler than oil-filled coils, promoting a longer life. The widely spaced cap terminals help to prevent crossfire, which is a common problem with smaller diameter caps. The amperage draw against the battery is minimal, pulling only 2-3 amps, whereas other aftermarket ignition systems can draw 10-or-more amps. For those racers using a total loss electrical system (no alternator), this prevents major voltage drop in the battery.

Last Thought

We were reminded that these distributors are built per-order, so the proper attention to quality and detail for each order is held to the highest caliber. Because of this, orders can take several days before shipping out. For more information on these or other ignition products from Performance Distributors, visit them online at

Article Sources

About the author

Bobby Kimbrough

Bobby grew up in the heart of Illinois, becoming an avid dirt track race fan which has developed into a life long passion. Taking a break from the Midwest dirt tracks to fight evil doers in the world, he completed a full 21 year career in the Marine Corps.
Read My Articles

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