Timing Advance
Ignition Timing Advance
In fuel-powered internal combustion engines, ignition timing refers to setting the time for a spark to occur in the combustion chamber in relation to piston position and crankshaft angular velocity. As a result of 
the piston movement and ignited by the spark plug, an air-fuel mixture enters the cylinder through valves. This mixture is supposed to be ignited before the cylinder reaches the top dead center (TDC). As a result, the gases will expand and force the cylinder down. But, ignition is usually delayed as the air-fuel mixture will take time to burn. If you advance the ignition timing, ignition will occur before the piston reaches top dead center. Timing advance is the number of degrees before the top dead center when the air-fuel mixture will be ignited in the combustion chamber. It is expressed in degrees before top dead center or °BTDC.
Setting the correct ignition timing is necessary for the long life and performance of the vehicle. It will help the detonation of the air-fuel mixture at the precise time. If the ignition timing is excessively advanced, the detonation will occur prematurely which will damage the engine in the long run. If the timing is excessively retarded, it will affect engine performance and fuel mileage. If the engine speed increases, the ignition timing has to be advanced more in relation to top dead center. When the speed of the engine increases, the air-fuel mixture gets only a limited time to burn; but, the burning process also goes on with the same speed as that of the engine. Hence, burning has to start early to detonate at the right time.
Most of the vehicles have advance timing between 10 and 20 °BTDC. You can find out the timing advance for your vehicle by referring to the vehicle’s service manual or you can contact your dealer and ask him. A timing light is used to change the ignition timing.
Typically, there are two types of ignition systems: mechanical ignition systems and computer controlled ignition systems. In mechanical ignition systems, usually, two methods are used to advance the ignition timing: mechanical timing advance and vacuum timing advance. The law of inertia is used to mechanically advance the ignition timing when the engine speed increases. This is also known as centrifugal timing advance. Vacuum timing advance uses manifold vacuum sources to advance the ignition timing. The latest engines use computerized ignition systems incorporated into an engine control unit. The computer controls the ignition timing.
Typically, vehicles come from the factory with an ignition timing that is set between the preferred ranges. It is possible for the user to advance the ignition timing to the maximum allowed range. This will provide more mileage. When you advance the timing, you are in fact increasing the compression in the piston chamber before the air-fuel mixture detonates. The more the compression, the more HP you get, and the fuel burns more completely. You can yourself change the ignition setting of your vehicle if you follow the directions provided in the service manual.