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Ignition overview >> ignition firing order >> ignition glossary

Porsche 911 Engine Ignition

Automotive Ignition Systems Overview

An automotive ignition system is an integral part of engine operation. The ignition system’s goal is to provide a high voltage spark for efficient burning of the fuel/air mixture for the engine’s combustion or power cycle.

The requirements for ignition are quite demanding. Relatively low voltage (typically 12 volts) has to be converted to extremely high voltage for spark. This occurs thousands of times per minute. Also, the voltage has to be delivered with perfect timing, which varies with engine rpm. In addition, the voltage needs to be transmitted in a hot, vibrating, and otherwise hostile environment. It is amazing that the ignition system can fulfill all these requirements so reliably.

Ignition system components

we have ignition An automobile’s ignition system is commonly accepted as broken into to two areas: the primary side and the secondary side. The primary side of the ignition is the low voltage side, where the battery is the source of power. The secondary side is the high voltage side, where high voltage is distributed from the ignition coil to the spark plug electrodes.

The primary side uses the battery, which is 12 volts on the early 911’s. Earlier vintage cars like the Porsche 356 had 6 volt systems. The battery power is controlled by the ignition switch. That means, with the ignition switch on, battery power is available for the ignition triggering to the coil.

Coil

The coil has a very important roll in ignition and is actually part of both the primary and secondary side. The coil’s job is to transform low voltage to extremely high voltage. The coil receives 12 volts from the battery, but delivers up to 15,000 volts or more, depending on the ignition triggering. How does it do that? The answer is…PFM!… Well, maybe not PFM.

The answer lies in the construction of the coil. The coil is an induction device and is composed of an iron core wrapped with a relatively thick primary coil of wire around it a few hundred times. There is also a much thinner secondary coil of wire wrapped around the primary winding at the ratio of approximately 100:1.

When current is applied to the primary winding it creates a magnetic field in the coil. Breaker points or an electronic ignition module triggers ignition by breaking the circuit on the primary side. At the moment this happens, the magnetic field on the primary winding rapidly collapses, and in so doing, it induces a very high voltage in the secondary winding. This high voltage transmits from the coil to the distributor, then the spark plug wires, and ultimately the spark plug electrodes.

Always consult a maintenance manual for reference to proper procedure.

Ignition overview >> ignition firing order >> ignition glossary