Q: I‘ve owned a few vehicles, but I’m new to engine tuning and automotive mechanics in general. What can you tell me about ignition timing? In particular, how does advancing or retarding the timing affect performance? And what variables might affect where my timing should be set?
A: Measured in crankshaft degrees, ignition timing refers to the position of the piston when the spark plug fires. The proper timing of this event will ensure good power and efficiency from your engine. So let’s take a look at what makes for “proper timing.”
Proper ignition timing ignites the air/fuel mixture just before 0 degrees (Top Dead Center) of the compression stroke. This gives the burning mixture sufficient time to do the maximum amount of work on the combustion stroke. If timing is set too early (advanced), the expanding ignition gases work against the piston, slowing it down. This can also produce a pinging or knocking sound. On the other hand, if your timing is too late (retarded), the expanding gases are chasing the moving piston down the cylinder, failing to produce maximum power. As engine rpm increases, timing must advance since there is less time for the combustion process to take place.
While variables like air/fuel mixture, fuel type, octane level, ambient air temperature, and humidity can all affect optimum ignition timing, a change in cylinder pressure delivers the most significant impact. As cylinder pressure increases—from higher compression ratios, engine load, or power adders like boost and nitrous oxide—combustion time is reduced and timing should be retarded.
Hope this information provides a good overview of the ignition timing process.