In the first part of our ignition story, we walked you through the basic components of the ignition system to get a better understanding of their function. In this article, we discuss a few more advanced components, their operation, and options available for racing. We take a look at the latest dirt track ignition components as well as some of the proven favorites.
Dirt track racing engines get put through the ringer lap after lap. Most engines are screaming at high-RPM, close to redline for the majority of the race. Not only does an engine need to handle the high revolutions, but the ignition system must also be up to the task of producing a full-power spark millions of times throughout a race.
There are many obstacles working against the ignition system, from the mechanicals of spinning the distributor and getting the spark to the right terminal on the cap at the exact moment to fire the gasses entering the cylinder, to the system’s ability to recover and produce a powerful spark moments after the previous spark. It’s an amazing feat of electronics and mechanics working together.
The most popular choice in many racing classes is to run a Capacitive Discharge Ignition, usually referred to as a CD ignition. MSD, FAST, Mallory, Pertonix and other companies offer CD ignitions. The benefit is an extremely powerful spark capable of running upwards of 10,000 rpm without breaking down.
The challenge for most inductive ignitions on race engines is to be able to charge up to full power between firings – a CD ignition solves that issue. Standard ignitions rely on the coil to build up the voltage through inductance (dwell time), but at high-RPM there’s less time to accomplish this feat, resulting in a lower output spark. Less spark power means the combustion event will be weaker, resulting in less power and even a high-end miss.
By drawing its supply voltage straight from the battery, the capacitor of a CDis nearly instantaneously fully charged to deliver a full voltage spark throughout the entire RPM range of a race engine. This is the main reason CD boxes are commonplace in racing.
CD ignitions have been around for many years and each company has their own twists and features which set them apart. The brand you chose is mostly up to the racer, perhaps for sponsorship or contingency awards. Most of the ignitions available will have an adjustable rev limiter which is a nice feature to have in the event of driveline failure or a missed shift.
At the PRI show, we saw a unique take on the CD ignition box in MSD’s 6CT ignition. This unit has several unique features just for the dirt track racer. The first thing you notice is a large LED display used to set the RPM limit. Not only does this provide an accurate RPM control, but it is used by the tech team to review the highest RPM reached during the previous event. The box also has tamper-proof screws and is fully potted to stand up to the rigors on the track.
Another benefit of running a CD ignition is the ability to trigger it with the distributor of your choice. The ignition still requires a trigger source like a magnetic pickup which is commonplace in most billet distributors. Also, a crank-trigger can be incorporated to produce a more accurate signal.
Five CD Ignition Facts You May Not Know
- CD ignitions are internally regulated, meaning it doesn’t matter if you feed 16 volts or 12 volts into them, their output stays consistent. However, when that input voltage from the battery drops below 12 volts, the ignition output will suffer.
- As a rule of thumb, most CD ignitions require 0.7 – 1.0 amp per 1,000 rpm (more once battery voltage drops).
- If you’re not running an alternator, it’s safe to run a fully charged 16-volt battery with a CD ignition. However, once that voltage drops down below 10 volts, the output of the ignition is going to suffer.
- Nearly all CD ignitions on the market today use a microprocessor to manage the spark delivery and behind-the-scenes controls. There are still a few ‘analog’ boxes available, but component obsolescence is coming into play.
- A CD ignition delivers a short-duration, high-voltage spark. To help at lower speeds, engineers provide the ability to fire multiple times since there is more time. A rule of thumb is three sparks for 20-degrees of crank rotation up until about 3,000 rpm.
When it comes to picking up the most accurate trigger signal possible for an engine using a distributor, a crank-trigger is the right choice. A crank-trigger system positions the trigger pickup off the front of the crankshaft which is more accurate, especially at high-RPM. There is a lot of mechanical flexing, twisting, and moving in the engine between the chain or belt-driven crank-to-cam gears all the way through the camshaft, only to be met by two more gears. With a crank trigger, all of those mechanical variances are avoided producing a more accurate trigger signal.
Crank triggers have been more popular in Dirt Late Models and FAST offers a system for small-blocks running a 7- or 8-inch balancer. The FAST kit is supplied with a precision machined-aluminum wheel that measures only .125-inch thick. There are four equally spaced tabs on the wheel that provide the trigger signal of their unique inductive pickup. The pickup is based on an OEM design and easily mounts to the engine with the supplied billet mounts. With the timing signal coming straight from the crank, the CD box will have the most accurate trigger signal available. Note that a CD ignition is required to use a crank trigger.
Tried And True But Still Improving
The venerable GM HEI Distributor is still a favorite (and mandated in many classes) distributor when it comes to dirt track racing. Really, what’s not to like – they’re inexpensive for budget classes, easy to upgrade, and simple to install with one main power wire to get your engine running. Who would have bet a distributor that GM introduced in the early-’70s would still be going strong in race engines today?
That doesn’t mean the technology has stayed the same all these years. Ignition companies have developed higher-output coils, ignition modules with improved dwell-control to increase the spark energy at higher-RPM, and even the centrifugal advance has been tweaked and tuned over the years. In fact, MSD Performance introduced the Circle Track HEI Distributor with a trick advance assembly. For racers who want to run an advance, the chromoly weights and cam plate are there, but if you prefer to lockout the timing, they provide a simple-to-install plate that slides over the weight pins to lock the timing. No more banging the gear off and welding.
Another company focused on the development of HEI Distributors is Performance Distributors. It’s been working with HEI’s for years and even offer the GM-designed distributor for Ford and Chrysler applications. They offer a number of upgrades for racing such as their proven 602-604 DUI model for spec engines. Each distributor is supplied with its high-output Dyna-Module and racing coil, a melonized gear and most importantly, an aggressive timing curve to match the requirements of these engines.
Track Imposed RPM Limiter
To keep racing close, costs down, or simply perform a check on racers’ setups, sometimes a rev limit is imposed in certain classes. MSD has worked with many tracks over the years and developed and external RPM limiter specific for an HEI ignition.
The MSD Digital Soft-Touch HEI Rev Limiter (PN 8727CT) plugs into most HEI distributors and provides the ability to set a rev limit from 3,000 – 9,900 rpm via two rotary dials. A unique feature of this rev limiter is the LED will display the highest RPM reached during the previous race. This is useful information for the race team, as well as tech officials. Also, if any connection to the distributor is lost or manipulated, a fault code will be displayed.
Tips For Coils And Bullet Proofing
Whether you’re running a CD ignition or an HEI distributor, it’s important to run the coil designed for each system. Engineers can futz (which is a very technical engineering term) with the winding ratios and even the resistance of the winding materials to manipulate the spark output. Coils can be created specifically for HEI/inductive ignitions with long spark duration, or to deliver a wallop of high voltage with less energy to follow through.
When it comes to choosing a coil, unless you have a way of really testing each coil and box combination, it’s best to stick with the coil recommended by each manufacturer to achieve the best spark output. Plus, some coils are designed to run at high-RPM for a long time which generally requires a more efficient design with effective heat dissipation.
Other areas to be concerned with are preparing your ignition system for longterm battle. Grounds are extremely important. You should consider running the ground wire of the ignition directly to the block or even cylinder heads. When it comes to the trigger-pickup wires from the distributor or crank-trigger, it is recommended to run a shielded cable to protect against any erroneous interference or hiccups. All ignition companies offer a shielded cable.
Plug wires are another area where a little effort goes a long way. Adding a protective layer of heat shield on the wires will keep a wire from melting on a header tube. Also, taking the time to route the wires through a quality set of looms will ensure they’re not flinging around under the hood. Dirt track racing is brutal on plug wires and underhood components. The more you can do to protect the wires and plug boots, the more you can relax or worry about another system on the car – like the fuel system.
Pro Tip: Even as sealed and tight as most CD ignitions and coils are these days, try not to blast the distributor, wires, or the boxes with the power washer after a race. Ignitions just do not like water.