How to Build Racing Engines: Ignition Systems

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
  • Distributor
  • Pickup
  • 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.

Robust ignition systems are essential for engines to deliver maximum horse¬power. Components include a precision calibrated distributor, top-quality wires, and spark plug boots all driven by a powerful coil and amplifier.

Robust ignition systems are essential for engines to deliver maximum horse¬power. Components include a precision calibrated distributor, top-quality wires, and spark plug boots all driven by a powerful coil and amplifier.

 

Digital ignition components like MSD’s Digital 6AL and Power Grid system controller provide digital tuning convenience and full control of an engine’s ignition requirements via computer software and a laptop interface.

Digital ignition components like MSD’s Digital 6AL and Power Grid system controller provide digital tuning convenience and full control of an engine’s ignition requirements via computer software and a laptop interface.

 

This MSD race distributor accom¬modates individual cylinder timing adjustment by mechanical means. Note that each individual trigger can be adjusted by loosening the appro¬priate screw.

This MSD race distributor accom¬modates individual cylinder timing adjustment by mechanical means. Note that each individual trigger can be adjusted by loosening the appro¬priate screw.

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.

 
 

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Ignition Choices

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.

Magnets embedded 90 degrees apart in this MSD crank trigger wheel create an electrical current every time they pass by the pickup coil. This triggers the ignition module to discharge the coil at the appropriate time. Crank trigger systems provide exceptional timing accuracy because they read directly off the crankshaft.

Magnets embedded 90 degrees apart in this MSD crank trigger wheel create an electrical current every time they pass by the pickup coil. This triggers the ignition module to discharge the coil at the appropriate time. Crank trigger systems provide exceptional timing accuracy because they read directly off the crankshaft.

 

Many circle track venues limit ignition systems to stock-type systems that incorporate minimal changes like a cap and rotor and a high-energy coil as found in this HEI unit from Performance Distributors.

Many circle track venues limit ignition systems to stock-type systems that incorporate minimal changes like a cap and rotor and a high-energy coil as found in this HEI unit from Performance Distributors.

 

The pickup coil is adjusted to within about .060 inch of the trigger wheel to provide a strong signal when the magnet passes by it. Ignition tim¬ing is set by loosening the pickup coil-mounting bolts and sliding the assembly up or down to achieve the desired timing.

The pickup coil is adjusted to within about .060 inch of the trigger wheel to provide a strong signal when the magnet passes by it. Ignition tim¬ing is set by loosening the pickup coil-mounting bolts and sliding the assembly up or down to achieve the desired timing.

 

Space limitations caused by the use of tunnel ram intake manifolds often require the use of low-profile crab cap–style MSD distributors that fit within the tight space behind the rear intake runners. The crab caps have the added convenience of placing the correct terminals on each side of the engine for easy plug wire installation.

Space limitations caused by the use of tunnel ram intake manifolds often require the use of low-profile crab cap–style MSD distributors that fit within the tight space behind the rear intake runners. The crab caps have the added convenience of placing the correct terminals on each side of the engine for easy plug wire installation.

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.

 
 

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Spark Plugs

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.

Larger-diameter distributor caps are generally preferred to help prevent spark scatter by placing the terminals farther apart. The low-profile crab-style cap is smaller in diameter, but made from the best materi¬als so spark scatter is not an issue.

Larger-diameter distributor caps are generally preferred to help prevent spark scatter by placing the terminals farther apart. The low-profile crab-style cap is smaller in diameter, but made from the best materi¬als so spark scatter is not an issue.

 

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.

High-voltage coils are essential to provide reliable spark energy in a high-compression, high-RPM environ¬ment. Coils like this MSD HVC II unit produce in excess of 44,000 volts with great consistency.

High-voltage coils are essential to provide reliable spark energy in a high-compression, high-RPM environ¬ment. Coils like this MSD HVC II unit produce in excess of 44,000 volts with great consistency.

 

Race-quality plug wires are necessary for adequate spark energy to the plug. To ensure best results use 8-mm or larger high-quality wires as shown in this MSD selection. For added protection, cover the boots and wires with tempera¬ture-resistant sleeves.

Race-quality plug wires are necessary for adequate spark energy to the plug. To ensure best results use 8-mm or larger high-quality wires as shown in this MSD selection. For added protection, cover the boots and wires with tempera¬ture-resistant sleeves.

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.

MSD’s Pro Billet series racing dis¬tributors feature larger-diameter caps and adjustable collars to aid in setting up the correct distributor depth for proper oil pump driveshaft engagement.

MSD’s Pro Billet series racing dis¬tributors feature larger-diameter caps and adjustable collars to aid in setting up the correct distributor depth for proper oil pump driveshaft engagement.

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

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