The spark inside your race engine is pretty simple, high voltage is used to jump a gap and create the heat needed to get combustion started. The spark itself is pretty simple, but getting everything to happen just right isn’t that easy. Spark timing is one of the most critical tuning agents we have to maximize power. If it isn’t right within a degree or two, power can be down. With the stiff competition of today’s racing, a loss of power because of bad tuning is unacceptable. We work too hard for every tenth of horsepower to have it lost from what could easily be avoided.
Our ignition systems are pretty simple, just a handful of components carry out the tough job of getting your mixture lit. The flywheel, coil, spark plug wire, and spark plug are the major components we have to work with. These components are very reliability, and as long as we get the engine timed right, the set it and forget it theory applies.
The purpose of the ignition system is to start the burn of the air/fuel mixture inside the combustion chamber at the perfect time. This allows the fuels energy to be converted to heat, which ultimately expands and pushes the piston down the bore. It is critical that this process is started at the correct time, otherwise this expansion process will happen too late or early and the piston descending down the bore will not be able to utilize its maximum energy. When the spark plug lights the air/fuel mixture it doesn’t cause an explosion. It actually causes the start of a controlled burn that starts out slow, rapidly increases to a fast burn rate, and then slows again before it burns out. Maybe it is easier to picture as a pile of wood that has started on fire, it takes a while to get going, burns like crazy once the fire has spread across the logs and then slows down as the last little bit is burned off.
Getting away from the thought that the mixture inside your engine is exploding can greatly help you develop horsepower and better understand ignition timing. By understanding the mixture burns at a slow rate, compared to an explosion, and knowing that by increasing this burn rate you can increase power output, you can use this to help maximize power.
Getting the mixture inside the chamber to burn faster increases the pressure rise in the chamber and makes better use of the expanding fluid. How do you increase the burn rate? Think of a forest fire on a calm day, though it burns, it doesn’t spread very fast. That is until the wind picks up, then the flame spreads uncontrollably fast. Now compare this to the air/fuel mixture burning inside your engine. The intake charge enters the bore and the valve closes, if the mixture is completely still when the spark occurs it will burn slowly out to the cylinder wall. Now picture the intake charge coming into the bore swirling around the bore axis. As the piston comes up the bore, the mixture between the flat part of the chamber and the piston get squished out towards the spark plug. Because of thoughtfulness in the design, the mixture motion in this example is very high. Now when the spark plug lights the mixture inside this small hurricane a new meaning is given to the name wild fire.