With modern coil and module...
With modern coil and module designs, Performance Distributors' HEI ignition is capable of providing adequate spark to a race car engine up to 9,000 rpm.
The biggest problem with racing stock cars is that sometimes the stock stuff tends to get in the way. It's no secret that when designing a new car, engineers at the Big Three aren't too concerned about how well they will perform on the oval track on Saturday night. Other concerns such as fuel economy, comfort, government regulations, and production costs are usually much higher on the priority list. That's fine for over-the-road cars, but as racers we are concerned with two things: performance and durability (in that order). So when the rules require the use of stock or stock-style replacement parts, that can sometimes cause problems.
One example is the HEI ignition. HEI stands for High Energy Ignition, and it definitely was when it was first produced; since then technology has passed it by. General Motors began selling its cars with an HEI ignition around 1975. At the time, HEI technology offered a few big advantages over other systems. Mainly, it was simple. Because the coil was actually inside the distributor cap, the HEI was easy to install and required the connection of only one 12-volt wire. Plus, it provided good energy output up to around 5,000 rpm, which was around the redline for most cars and trucks anyway. As a result, the HEI was nearly ubiquitous in all of the General's cars and trucks with V-8 engines until the mid-'80s.
If you race a car in a stock class and the car was produced by GM, you are often stuck with the HEI ignition. While it was nearly perfect for street cars, an HEI struggles to provide an adequately strong spark at higher rpm levels. Because of this, many race engines using a stock HEI develop a high-speed miss around 5,500 rpm that essentially acts as a rev limiter. The poor spark qualities developed by the ignition at that engine speed means the air/fuel charge fails to ignite occasionally in the cylinder. From the driver's seat, the engine feels like it's falling on its face.
Fortunately, you do have options at your disposal. Companies specializing in performance applications, such as Performance Distributors, have developed HEI ignition systems that are incredibly powerful and ideal for many racing applications (whether your rules require you to run an HEI ignition or not). Modern coil and module designs are capable of providing enough spark to ignite a high-compression, high-revving engine in even the worst conditions. The inherent simplicity of the design is still a plus for racers. What racer doesn't appreciate any component that's easy to install and eliminates wiring clutter?
Because Chevrolets are so...
Because Chevrolets are so prevalent in Street Stock racing and because GM used HEI ignitions in almost every V-8 it built between the mid-'70s and the mid-'80s, most Street Stock racers have to deal with a stock ignition that cannot deliver enough spark at the upper rpm levels.
Stuck with Stock If your tech inspector is a real stickler and won't accept anything beyond a stock replacement HEI, there are a few things you can do. Purchase a new HEI to make sure it is in optimum working order, and perform a few basic modifications. First, block off the vacuum advance mechanism. It isn't necessary for racing applications. Kits are available from many sources that use a small plate to block off the vacuum advance. If you are running a stock ignition, you probably will want to do the same thing with the mechanical advance. On a high-quality ignition built for racing, the mechanical advance is usually dependable enough to be helpful. On a stock system, the fit and finish is haphazard and the pieces can often stick. The mechanical advance can stick when the hinge points on the throws become worn or the springs break. Stock springs on the mechanical advance are also usually far too weak anyway and allow full advance at engine speeds that are even below what you will run during caution and warm-up laps.
Like the vacuum advance, kits are available that allow you to easily lock out the mechanical advance mechanism. You can also simply just tack weld the weights in the closed position. Once that is done, set your ignition timing so that your engine performs best in the racing rpm range, and forget about it.
Finally, if you absolutely must race a bone-stock HEI ignition, you should also make sure the rest of the ignition system is operating as efficiently as possible to help things along. Steve Davis of Performance Distributors has performed an untold number of tests on all types of ignition systems and recommends carefully monitoring your plug gaps to delay the inevitable high-speed miss as long as possible. "On a stock HEI, you cannot go over about 0.040 or 0.045 inch of plug gap," he says. "The more plug gap you have, the more complete burn of the air and fuel mixture you will get, but it also takes more power to get the spark to jump that gap. On our racing HEI ignitions, we like to run plug gaps between 0.050 and 0.055, but you have to have a coil and module that's strong enough to jump that gap or else it will cost you some problems. On a stock system, you cannot get it to jump a gap that large and you will wind up with a severe miss. So you have to keep your plug gaps tight and just live with it."
You can also invest in a good set of plug wires with low ohm resistance and, although it can cause a horsepower drain, keep an alternator on your car so the ignition is supplied with all the power it can use.
Performance Distributors locks...
Performance Distributors locks out the vacuum advance with a plate on almost all its racing distributors because it simply isn't necessary. One option that the company does offer is a distributor with an "Instant Timing Knob."
Purpose-built for racing On the other end of the spectrum is the distributor that's built specifically for racing. In many stock-level racing classes, all that's required is the same type of ignition the car originally came with, so an HEI purpose built specifically for racing is perfectly legal.
The greatest difference is a racing HEI uses an upgraded coil and module capable of powering the engine to 8,500 rpm and beyond. An HEI is an inductive discharge system, meaning the 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 raises the energy level and sends it to the distributor, which then routes it to the appropriate spark plug.
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 of that energy to the spark plugs. More energy at the spark plugs gives you the option of opening up the plug gaps the way Davis spoke of.
The ignition module is the equivalent of the system's brain. It controls the current sent to the coil. Obviously, if the coil is fed a higher current, it can continue to send the appropriate amount of energy to the plugs at higher rpm levels. It is also possible to use the module to increase the duration of the spark and even act as a rev limiter.
Two nylon screws are used...
Two nylon screws are used to hold the rotor in place because they reduce the chances of a spark arcing around inside the cap, unlike metal screws.
"On the module side, we are putting 2 to 3 more degrees of dwell time in it throughout the rpm range to get more power out of it," Davis says. "You have to be careful, though. You can't go crazy with it and crank in 10 more degrees of dwell throughout the rpm range or you will saturate the coil so much you will burn it out. With the coil we can trick it out with the windings to increase performance. We can change it so that it can maintain the spark at the higher rpm levels. But you have to design the module and the coil so they work together as well as possible.
"Together, we can design an HEI ignition that will fire all the way to 9,000 rpm effectively if a guy is running an alternator," he continues. "If he's just running off the battery, it will go to 8,500 rpm. We can design a coil and module that will go to a higher rpm if we wanted to, but nobody turns that many rpm."
Advance Issues Many racers prefer to race with the ignition's advance mechanism locked out because they prefer the simplicity and fear that the mechanism will fail at an inopportune time. If you are racing a bone-stock ignition like we mentioned earlier, that's not a bad idea, but Davis says if you are running a quality racing piece you are leaving performance on the table.
"We recommend not locking out the advance for two reasons," he says. "First, it makes the engine hard to start. Second, a lot of times guys don't need full advance at the rpm they are running. If they are bunched up in a pack and they aren't at wide-open throttle, having the ignition locked at full advance can really be tough on a motor. Getting the right weights and springs in there with a quick rate of advance gives you the best of both worlds.