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2. Why does an MSD produce multiple sparks and what are the benefits? Conventional CD ignitions supply one spark of intense energy but for a short duration (time). An MSD uses multiple sparking technology to take advantage of the quick rise time and power of a CD Ignition by producing a series of sparks. More sparks equal more heat in the combustion chamber resulting in complete combustion of the fuel mixture which produces more power. At lower rpm, there are many benefits to multiple sparks including a smoothidle, improved throttle response plus the spark series prevents fouling plugs or fuel loading up in the cylinder when air/fuel distribution is poor. The multiple spark series of an MSD Ignition Control lasts for 20° of crankshaft rotation. At lower rpm, 1,000 rpm for example, there is plenty of time to fire the plug a number of times to ensure ignition of the fuel mixture. As rpm increases, the piston travels up on the compression stroke faster resulting in a shorter amount of time available to fire the plug so the number of sparks that occur decreases. By about 3,000-3,300 rpm, there is only enough time to fire the plug once. From about this rpm range on, an MSD ignition control delivers one intense, full power spark.
3. What is the best spark plug gap for my application?
The spark plug is the point in the ignition system where electrical energy is converted into heat, consequently, the larger the gap the greater the amount of heat available to light the air/fuel mixture. However, too large of gap com- bined with increased cylinder pressures can put excessive pressures on the initial voltage needed to ionize (cross) the gap. Finding the optimum plug gap for your application is best determined by experimentation because there are so many engine variables to consider.
An MSD Ignition Control has enough output power to consistently fire wider spark plug gaps on a performance engine. As a starting point, follow the engine builder or manufacturer’s recommendation for the plug gap. With that, you can experiment with increasing the gap until the best performance is found.
As a rule of thumb, it is recommended to increase the plug gap by .005” - .010” followed by testing and tuning. Keep in mind that larger spark plug gaps also place increasing demands on the secondary portion of the ignition system including the distributor cap and rotor, coil wire, and spark plug wires. They should all be in top condition and checked periodically during the race season. Remember that electricity takes the path of least resistance to a ground so if the gap is too large the spark may short to another point with less resistance.
4. What size battery do I need if using an MSD ignition?
The battery is the fuel tank for the ignition system (magnetos excluded). When it’s empty there is no electrical power available for the ignition system to convert into heat at the plug gap. In long duration racing events such as circle track racing, an alternator is highly recommended. In drag racing, a charging system is not a complete neces- sity as long as you have a good battery and charge it in between each round. Also keep in mind that electric fuel and water pumps, fans and solenoids eat up a lot of current as well.
Race cars without charging systems must have a battery with a large enough capacity to power all the electrical parts. For example, an MSD 6 or 7 series ignition consumes approximately one amp per thousand rpm, so at 5,000 rpm the MSD alone is using five amps. An MSD is designed to produce full power sparks with a supply voltage of 10 volts, but if the supply drops below that, ignition output will suffer.
An MSD can be used with 16 volt batteries, but no performance gain will occur because the output power of the MSD is regulated. The advantage of a 16 volt battery is increased electrical capacity. For more information on battery requirements with an MSD, ask your MSD Customer Support Tech for our Battery Tech Bulletin.
5. What do you have to replace my points distributor and what are the advantages with electronic versus points?
MSD does not have a module to replace the breaker points system in your stock distributor, however an MSD Ignition Control will work great with a points trigger ignition. In fact, if you replace the points when you install your MSD, you’ll probably won’t have to replace or adjust them for years! The MSD’s trigger wire connects directly to the breaker points wire so when the points open, the MSD is triggered. Since the MSD’s capacitor is responsible for sending the spark energy to the coil, the points are only used as a trigger reference signal. With this connection there is very little current crossing the points so the wear is nominal at best. Also, the MSD controls the dwell so the adjustment of the points is not that critical either. This setup works great with street cars and budget racers, but when you begin stepping up performance more and more, the need for a quality distributor comes into play.
MSD’s Pro-Billet Distributors are engineered to deliver precise trigger signals, provide accurate distribution of the sparks and are reliable. A magnetic pickup is used to trigger the ignition. Unlike points, this pickup is maintenance- free and is capable of accurate trigger signals throughout 10,000 rpm.
6. What is the best Timing Curve for my car?
There is no real way for our Techs to answer this question but they can point you in the right direction. It takes testing and tuning time to find the best curve that fits your application. Many variables affect the ignition timing curve such as compression, cam specs, intake system, fuel, exhaust, altitude, driving habits and so on. The chart on page 3 lists some factors that will help you determine what sort of timing curve you should work towards for your specific application. MSD’s mechanical advance mechanism is accurate and easy to adjust so you can try different combinations with the supplied springs and stop bushings. We also offer a variety of electronic timing controls so engines with locked out timing or crank triggers can take advantage of altering the timing as rpm changes.
Note: When you are testing different curves, listen for detonation (spark knock) which is a sign of over-advanced timing.
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