The essence of ignition timing, whether it's static or dynamic, is to ensure the spark igniting the fuel vapors happens at the correct time. "Correct," however, is a shifting target.
Imagine an engine piston rushing up its bore during the compression stroke. Fuel is injected into the bore and gets compressed as the piston rises. At or near the top of the stroke, the spark plug fires and the fuel ignites, pushing the piston down. It's a simple process, but one that needs to account for how long it takes for all the fuel to ignite in relation to when the piston will reach top dead center -- the point where the piston and cylinder head is smallest and exploding fuel will have the most power and most complete burn.
With the above factors in play, the ignition must be timed so the spark begins the fuel burn sometime before top dead center, or BTDC in engine parlance. This is measured in degrees of rotation. Most engines set ignition timing somewhere between zero and 20 degrees before top dead center. This is called base timing. When set, the ignition system and engine are timed so the fuel in a cylinder is at its peak burn just as the piston compresses the fuel vapors into the smallest amount of space.
Most cars will run fine with timing a few degrees off from ideal. But further refinements are needed to reach a point where the engine is running at peak performance and has the fewest exhaust emissions.
Before delving into any type of ignition timing, check the engine to see if all of the systems are working correctly. If other systems related to the engine and ignition are not working right, then it's likely that the timing will need to be reset once other problems are repaired. It's best to set timing on a car in top condition, if possible.
Make sure to check:
- Spark plugs (condition and age)
- Spark plug wires or coils (condition and age)
- Distributor system (correct function and condition)
- Fuel injectors or carburetor
- Fuel pump and lines
- Battery condition and state of charge
- Overall engine condition
With the list checked and the car off, it's time start timing the ignition system ... almost. There is some information to gather before you get your hands dirty. We'll approach this in the next section.