Mallory's New Rev-Limiting Ignition Module

In today's Pontiac hobby, it isn't unusual to spend thousands of dollars on a high-performance engine. Like most wise hobbyists, we take precautions to ensure its longevity. This typically includes careful preparation of the original components along with careful machining and assembly--or even the addition of aftermarket pieces, as they are sometimes an improvement over the originals they replace.

While it's true that most aftermarket internals are designed to endure more power and engine speed than originals, they too were designed around intended limits. And anytime those limits are surpassed, catastrophic failure can result. But in many instances, excessive power isn't the killer, it's the severe damage that can result from grossly exceeding the engine's maximum operational speed.

This new product from Mallory Ignition gives anyone running an HEI distributor the benefits of a rev limiter in a matter of minutes. The No. 699 HyFire HEI module is a direct replacement for the original four-pin module and is adjustable from 5,000 rpm to 9,500 in 100-rpm increments. Available through most suppliers currently offering other Mallory products, this item retails for around $100.

Although the installation can be performed without removing the distributor from the engine, we chose to remove ours for photographic purposes. With the cap and rotor removed, here we see the original electronic components that will soon be replaced.

The first step is to remove the original module. This is accomplished by unplugging the two-wire lead from the pick-up coil and removing the two 1/4-inch-head bolts that fasten the module to the housing. The condenser assembly and wiring harness are then removed.

There is an answer for hobbyists who fear this type of damage--a control device that governs maximum engine speed known as a rev limiter. Produced by a number of aftermarket manufacturers, the most common limiters tie into the ignition system and regulate engine speed by canceling spark to alternate cylinders, creating a calculated high-speed miss that effectively prevents the engine from revving further.

Whether a stand-alone unit or part of a multispark ignition box, rev limiters have typically been a component, separate from the distributor, with its own wiring. And while savvy hobbyists have found ways to conceal its appearance within the engine or passenger compartment, others refuse to use one because of its nonstock appearance or what appears to be complex wiring. But we may have heard those types of complaints from reluctant hobbyists for the last time.

Mallory Ignitions has just released a new product for hobbyists running HEI distributors. It is an adjustable rev-limiting control module that replaces the original four-pin module and condenser without a single modification.

Follow along as we replace our original module with Mallory's unit and give ourselves some much-needed peace of mind while running our '76 Trans Am through the gears.

With the original pieces out of the way, we applied the white-colored heat-sink compound to the machined pad where the module sits. A small amount is supplied, and its use is critical since it allows heat from the module to dissipate into the aluminum housing. The new module is then set into place and secured by the two original module bolts and a screw that Mallory provides. Then the pick-up coil is reconnected. Installation is as easy as that!

A small series of switches controls the point at which the module begins limiting engine speed. The minimum setting is 5,000 rpm with adjustability toward its maximum of 9,500 in 100-rpm increments. Wanting to verify its accuracy at different speeds that might otherwise be unsafe for most engines, we tested ours on a distributor machine and found it begins canceling cylinders about 200 rpm lower than its programmed point. For instance, a setting of 6,000 rpm might begin around 5,700-5800 rpm, ensuring the engine cannot pass its set point. Once the module was installed in the car, we found the same. This may be something to consider when programming the module for your combination.

In 15 minutes we installed an adjustable rev limiter that is virtually undetectable with the cap installed. Once on the road, Mallory's module performed like the original it replaced. When we approached its programmed limit, it began canceling cylinders and prevented the engine from revving higher. Subse-quent dyno and dragstrip testing performed on a 500hp engine running well into the 11s in the quarter-mile has shown it performs at least as well as the original module. Although future adjustments do require removal of the cap, they can be completed in a minute or two. So if an adjustable rev-limiter that installs easily and looks stock for about $100 is something that appeals to you, look no further than Mallory's No. 699 HyFire module. It's a small investment for the amount it can save.