As a rule, racing ignition systems aren’t particularly complicated. All you need is a power source and a means of distributing a high voltage (spark) to each cylinder at the proper time. In reality, it is far more complex. Racing ignition requirements are complicated by numerous factors that require special consideration and specific hardware to ensure efficient and reliable performance. The wide range of possible operating conditions makes optimum ignition timing and delivery of adequate power to light the mixture vital parameters of overall engine efficiency, particularly when the system is challenged by high compression ratios, extreme engine speeds, and ever rising boost levels on supercharged systems.
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Selecting an ignition system for a racing engine requires consideration of several important factors. Since timing is the basis of all engine functions it is critical that, above all else, the ignition system maintain rock-solid timing integrity.
The ignition system consists of the following components:
- Battery (power source)
- Ignition coil
- Ignition module
- Plug wires
- Spark plugs
Each of these components require individual attention to ensure compatibility and successful operation. A full 12 volts of power is typically required for proper ignition operation. This makes the battery and its charging system vital contributors to successful ignition operation.
Modern racing ignition systems have largely moved to digital control to improve their accuracy and reliability. The triggering device may be located within the distributor itself or externally as in crank trigger ignition systems that rely on exact crankshaft position signal to trigger the spark in each cylinder.
Depending on the type of system, the triggering device may be a magnetic pickup, an optical trigger, or a Hall-effect transistor, which functions similarly to a magnetic pickup. Optical devices use an LED (light emitting diode) and a interrupter wheel to provide the trigger effect. The pickup sensor may be located within the distributor itself or externally as with a crank trigger system. Crank trigger systems are the most accurate because they eliminate timing inconsistencies caused by variables such as camshaft twist.
Digital controllers like MSD’s Power Grid system provide full access to all ignition functions via dedicated computer software that runs on a laptop computer. The Power Grid controller uses camshaft synchronization to provide individual cylinder timing alterations to compensate for varying cylinder conditions caused by fuel ratio or runner length inconsistencies and other conditions that may affect individual cylinder timing requirements. It also provides tunable launch and shift retard functions, rev limiter control, individual timing curves for each gear, and ignition data acquisition for post run evaluation.
Ignition control has never been easier and you have seemingly endless choices, but basic engine building practices still apply. You must take great care to ensure that the distributor gear and the camshaft gear are materially compatible, properly meshed, and well lubricated. Race distributors are equipped with an adjustable collar that allows you to control the depth of the distributor in the engine. This prevents bottoming the distributor gear against the internal oil pump shaft or meshing the gears too tightly. The collar also permits compensation for variations in manifold mounting-flange height.
The development of both multi-firing and extended-spark ignitions added unique capabilities to high performance ignition systems, particularly those that operate at engine speeds below 6,000 rpm. Instead of producing a single short spark for ignition these systems either produce multiple high-voltage sparks or one long-duration spark.
In multi-spark systems the number of sparks per ignition cycle at idle can be as many as six, when time between power strokes is the greatest. As engine speed increases, the number of sparks decreases to about two at high RPM. In extended-spark ignitions, a single, long-duration spark jumps the plug gap during the time a multiple-spark system would generate several sparks at the plug.
Potential horsepower increases from multiple-spark or long-duration systems depend on the flame propagation characteristics of the combustion chambers. Cylinder heads with larger chamber volumes can benefit most from these ignitions, and although it’s impossible to predict the benefits on any single engine, gains may vary from negligible to as much as 5 percent. Engines with small-volume chambers usually show little or no improvement from multi-firing ignitions. However, multiple-spark or longduration ignitions almost universally help smooth out a rough idle and minimize plug fouling that can hurt engine performance during the first critical seconds after leaving the starting line.
The current trend to smaller, shallower combustion chambers has generally reduced timing requirements for many engines and perhaps lessened the need for multiple- or extended-spark systems except perhaps in lower-tier applications that operate in the 4,000- to 6,500-rpm range.
The need for higher-energy systems with greater individual cylinder control has fostered a new age of precision ignition timing controllers that have revolutionized the precise control of racing ignition systems.
Other system designs found on racing engines include magnetos, crank-trigger systems, and more complex forms of MSD systems, including high-power multiple-coil ignitions with electronic advance curves, high-speed retards, and other exotica.
Magnetos have always been popular and reliable racing components. The faster they spin, the hotter the spark they produce. They are really a simple generator that operates without outside power. The instant a magneto begins to turn, it starts generating electrical power. If you have ever been the victim of the popular racer’s prank of spinning a magneto while holding the lead you know how much kick they can produce. At low RPM they barely have the energy to fire the plugs, so they are usually reserved for high-RPM, race-only applications.
Spark plugs for an engine should have the proper heat range, and they must be gapped to match the ignition system’s requirements. Greater secondary voltage often permits the use of a slightly colder plug. Dyno tests often indicate that plugs of one or two heat ranges colder than stock can produce an increase in power, although this may not occur in every case. In addition, a higher secondary voltage has more energy to jump across an air gap, so increasing spark plug gap by .010 to .020 inch may provide a fatter spark that more reliably ignites the air/fuel charge. This can be of particular help with lean mixtures or high compression ratios (but don’t exceed .050-inch gap since secondary voltages may go high enough to damage ignition components, and electrical emissions also dramatically increase). More reliable ignition can, in turn, increase the speed of flame-front propagation, and this may require slightly less total ignition advance to re-establish optimum power. This can be beneficial in reducing negative work against the piston before TDC. If the ignition timing is not optimized when the flame propagation times are altered, the result can be a reduction in power. A small change is usually all that’s needed, assuming the ignition advance was right-on prior to modifications.
Spark Plug Wires
Secondary wires used with modern electronic ignition systems must withstand higher voltage levels and prevent spillover into vehicle electronics, including engine-control computers. High-temperature silicone-jacketed wires are available for racing applications. MSD, Mallory, Moroso, and others make excellent 8-mm, heat-resistant cables that are substantially superior to the carbon-impregnated, stringcore versions that are supplied as standard equipment by many auto manufacturers. Protection can be added to secondary wires by jacketing them in tubing made of glass cloth that is highly resistant to heat, the most common cause of premature wire failure. MSD offers glass-cloth tubing and a self-vulcanizing silicone rubber tape that can be wrapped around the wires to secure the cloth tubing or to add more heat protection at critical points, especially around header tubing. High engine compartment temperatures bond the tape permanently to the ignition wires, improving their insulation resistance to both heat and high voltage.
Many speed shops sell a variety of great-looking colored plug wires. Some of these wires are much better suited to racing use than others. Carefully examine the core and the insulation before you buy. If they have a carbon-string core, either put them down or resign yourself to replacing them every year. Make sure the plug wires are insulated with temperature-resistant silicone rubber. Keep in mind that wire manufacturers can claim they use silicone insulation as long as the jacket material is composed of only some silicone rubber. Cheaper wire sets do not withstand racing-level heat radiated from headers. The best include top-of-the-line wires from MSD, Mallory, Accel, Moroso, and others designed for serious racing applications.
Race Engine Ignition Tips
A racing ignition system should generate a rock-solid timing mark at all engine speeds. There should be no visible signs of widening, spreading, or jumping. Most of these problems can usually be traced to several mechanical and/or electronic sources, but the most common causes are a loose timing chain, worn distributor bushings, or a sticking mechanical advance. In addition, since the oil pump is driven off the bottom of the distributor, spark scatter can often be traced to pressure pulses generated by the oil pump, especially when high oil pressure is used. Also, big-block and small-block Chevy V-8 racing distributors incorporate a pair of rubber O-rings around the base of the distributor just above the distributor gear. These seal the oil passage around the distributor and prevent loss of pressure due to excessive leakage.
As a rule, use spark plugs with the coldest heat range that support complete combustion without fouling under race conditions. Pay particular attention to the routing of the spark plug wires. Make certain that the wires do not touch anything (such as a hot header), and that they are actually routed as far as possible from any heat source that could damage them.
Power time the engine at a speed above the point of any mechanical advance, or at least 2,500 rpm if the advance is fully locked out.
Written by John Baechtel and Posted with Permission of CarTechBooks