The ignition system of a car is one of the most overlooked elements when it comes to engine modification and car tuning. Most people think that once their car modifications are done, all they need to do is get the ignition timing right, turn the ignition and they'll be on their way. But it's much more complicated than that. For one, the spark must be strong enough to ignite the air/fuel mixture. That might sound obvious, but what's not so obvious is that air molecules act as an insulator, and when you modify your car to get more air into the engine, the spark from the stock ignition system might be too weak to effectively ignite the air/fuel mixture, particularly if you're running a turbo or a supercharger. In fact poor spark quality can have as negative an effect on engine power as poor ignition timing. In addition, an air/fuel ratio of 11 parts air to one part fuel, which is a fuel rich mixture, is most conducive to spark ignition. However, the air/fuel ratio for the proper burning of the fuel is 14,7 parts air to one part fuel. Thus, the air/fuel mixture is not ideal for a spark ignition system, particularly during cold start conditions where fuel vaporization is not as effective.
Once the air/fuel mixture is ignited, the rate at which the flame passes through the combustion chamber becomes important if you want to unleash the maximum power from your engine. If the flame travels too fast, the resultant peak combustion chamber pressure will occur too early and would place tremendous load on the pistons, conrods and bearings while the piston is still moving up to top dead center (TDC); if the flame travels too slowly, not enough force would be generated to create maximum power at the wheels. There are three things that influence the rate at which the air/fuel mixture burns and the flame passes through the combustion chamber:
- The quality of the air/fuel mixture
- The movement or turbulence of the air/fuel mixture in the combustion chamber
- The design of the combustion chamber
We discussed the air/fuel ratio when we discussed the four strokes of the internal combustion engine; we discuss the movement of the fuel mixture in the combustion chamber and the design of the combustion chamber in our section on gas flowing and cylinder heads. What this leaves us with then, is to discuss the system that generates that flame, i.e., the ignition system. That is what we endeavor in this section where we'll discuss the different types of car ignition systems , including the inductive-discharge ignition system, which makes use of either a points breaker or a magnetic pickup, the capacitor discharge (CD) ignition system, and the distributorless ignition system, as well as their strengths and weaknesses, adjusting ignition timing for optimal performance, improving spark strength and quality by choosing the optimal spark plug and using the best spark plug gap, and techniques for modifying the car's ignition system to improve engine performance. But first we'll begin with getting a basic understanding of how the ignition system works in ignition system basics.