bkniep

Can some of the more technical folks on the board enlighten me? With all the tuning talk, this seems to be a major issue. What is it? What causes it? Does it happen with stock engines as well?

Thanks in advance.
Bill

Geoffrey

Ignition timing refers to the point in the 720 degree cycle where the spark plug is ignited. Once the spark plug is fired, it ignites the air fuel mixture. The flame speeds away from the spark plug and requires some amount of time before it is fully burned. This is what pushes the piston down the bore. You need to ignite the spark plug before the piston reaches TDC to allow for maximum pressure. Ignite the spark plug too early and detonation occurs, ignite it too late and the piston speeds away from the flame. Pulling timing simply refers to the reduction of ignition timing from before tdc to a point closer to tdc. This can be done by any number of tables within an ECU and depending what the sensors are telling it.

ca993twin

Geoffrey has a good technical explanation, but perhaps the implications aren't as clear. If your engine is reducing the ignition advance (pulling timing), you will be losing power. Too much advance is destructive to the engine (detonation). Just like Golidlocks... it has to be just right. Our engines are equipped with "knock sensors" that can detect detonation, and the ecu can take steps (reducing boost or pulling timing) to save the engine from damage. Running too low an octane fuel will activate the knock sensors and cause the ecu to take whatever steps are programmed. Our cars are designed for a minimum of 93 or 94 octane... more if they are modified. Here in California, the best you can normally get is 91. Bleech. There is a station here that sells 100 octane unleaded. Yummy.