The earliest petrol engines used a very crude ignition system. This often took the form of a copper or brass rod which protruded into the cylinder, which was heated using an external source. The fuel would ignite when it came into contact with the rod. Naturally this was very inefficient as the fuel would not be ignited in a controlled manner. This type of arrangement was quickly superseded by spark ignition.
Mechanically timed ignition
Most four-stroke engines have used a mechanically timed electrical ignition system. The heart of the system is the distributor which contains a rotating cam running off the engine's drive, a set of breaker points, a condenser, a rotor and a distributor cap. External to the distributor is the ignition coil, the spark plugs, and wires linking the spark plugs and ignition coil to the distributor.
The disadvantage of the mechanical system is the use of breaker points to interrupt the low voltage high current through the primary winding of the coil; the points are subject to mechanical wear where they ride the cam to open and shut, as well as oxidation and burning at the contact surfaces from the constant sparking. They require regular adjustment to compensate for wear, and the opening of the contact breakers, which is responsible for spark timing, is subject to mechanical variations. In addition, the spark voltage is also dependent on contact effectiveness, and poor sparking can lead to lower engine efficiency. Electronic ignition (EI) solves these problems. In the initial systems, points were still used but they only handled a low current which was used to control the high primary current through a solid state switching system. These contact breaker points were replaced by an angular sensor of some kind - either optical, where a vaned rotor breaks a light beam, or more commonly using a Hall effect sensor, which responds to a rotating magnet mounted on a suitable shaft. The sensor output is shaped and processed by suitable circuitry, then used to trigger a switching device such as a thyristor, which switches a large flow of current through the coil. The rest of the system (distributor and spark plugs) remains as for the mechanical system. The lack of moving parts compared with the mechanical system leads to greater reliability and longer service intervals. For older cars, it is usually possible to retrofit an EI system in place of the mechanical one. In some cases, a modern distributor will fit into the older engine with no other modifications.
MSD Ignition products are the finest ignition components you can install on your car whether it's a daily driver, dirt tracker, 4-wheel drive, a seven second Pro Stock car or Big Foot. MSD designs, develops, tests and manufactures the entire line of MSD products including Ignition Controls, Coils, Timing Accessories and Spark Plug Wires and Accessories. MSD, housed in three buildings includes four engine dynos, two chassis dynos, complete CNC and machining centers, modern shipping and packaging areas plus assembly and burn-in departments.