By the time you hear the noise, detonation has been going on for quite some time. Think about all the cast iron, sheet metal, and insulating material that sound has to penetrate before the driver actually becomes aware of it. Add a little middle-aged high frequency hearing loss to that situation, and it's possible some drivers won't be able to hear even severe engine noises before they start doing damage to internal parts. Chasing that mythical "ideal" timing advance setting is pretty much of a fool's mission! I've proved that to my own satisfaction on dozens of dyno runs. A tiny change in ambient temperature, gasoline quality, or relative humidity can throw even the most complicated of timing calculations a curve. We ran a series of dyno pulls on a round track engine one morning and had the engine dialed in well. Then we went to lunch and a thunderstorm came through the area, which changed the humidity. On the afternoon run, we lost 12 HP. "Your mileage may vary!"
Jerry
