An Easy Guide to Electricity in Your Car
Coils 201 - Advanced Coil TalkA commonly asked question is, "What is the best coil for my application?" Another similar question is, "Will this coil work for my application?" The answer to both of these questions is, annoyingly, "It depends." Here's how it works out: non-CD (or inductive storage) ignitions use the coil primary to store energy in a magnetic field. The amount of stored energy is a function of the square of the primary current. This means that, for example, if you double the primary current, you quadruple the primary energy. Because of this, the primary inductance and resistance are critical items. However, in answer to the obvious question of, "Why not make all coils for conventional ignitions with high primary inductance?" we have to deal with the fact that as the inductance goes up, the longer time it takes for current to rise when the points or transistor switch are "on". This means that at low speeds, you may have plenty of time to reach maximum current, but as the RPM goes up, you have less and less time available. In contrast, a lower inductance coil may have less energy at the same current rating, but will allow more current to build up at the higher engine speeds, and actually have more energy than the high inductance coil would. All inductive storage ignitions require some kind of current limiting to make sure that the primary current is not excessive at low speeds. In older point and electronic ignitions, a high-wattage ballast resistor was commonly used to do this. Typical values are .5 to 2 ohms. More modern systems often use some kind of electronic current limiting in the coil driver device itself to limit the current. The disadvantage of this is that, if the current is allowed to reach the limit, there is a lot of heat developed. CD ignition systems have a different operating condition. A CD system uses an internal DC to DC converter to step the battery voltage up to the 400-600 volt region. This energy is stored in an electronic component called a capacitor. When the trigger signal occurs, the stored energy is transferred to the coil, and the transformer action of the coil steps the voltage up high enough to fire the spark plug. This allows us to make the coil design relatively independent of the engine RPM range. However, the coil characteristics still affect the "quality" of the spark. Turns ratio still determines the open circuit maximum voltage. Since CD ignitions typically have primary voltages higher than inductive storage ignitions, the system maximum voltage is also higher (with the same coil). The turns ratio also affects the spark gap current in the same way, and the coil inductances and resistances also affect the risetime similarly. With a CD system, we can tailor the coil to match what we need more exactly.
Adding Modern Coil-Per-Cylinder Ignition to a Vintage EngineBy: Todd Ryden | 12/03/2020
Coil-per-cylinder ignition is the standard ignition system among new OEM vehicles, but with MSD's CPS system, you can bring the ignition system on your vintage V8 into the modern era.
Everything You Need to Know About Earl's AN Hoses and Hose EndsBy: Jeff Smith | 12/03/2020
Plumbing your car can be tricky and the copious amounts of Earl's AN hoses and hose-end styles might be a little intimidating at first. In this tech installment, we walk you through our most popular hoses and hose ends and explain how they work.