* Specific engine build: The camshaft profile, compression ratio, and other internal modifications significantly impact ideal timing. A stock engine will have different needs than a heavily modified one.
* Fuel type: The octane rating of the fuel used affects how much advance is safe without detonation (knocking). Higher octane allows for more advance.
* Ignition system: The type of ignition system (points, electronic, etc.) and its condition influence the accuracy and consistency of the spark.
* Altitude: Higher altitudes require slightly less advance.
Therefore, you cannot simply state a single number. You must consult the engine's specifications (if available) or use a timing light and carefully adjust the timing while monitoring for detonation. A properly equipped dynamometer is the best way to determine optimal timing, especially for modified engines.
For a stock, relatively unmodified Pontiac H.O. 455, a starting point might be around 34-36 degrees BTDC (Before Top Dead Center) at idle. However, this is just a *guesstimate*, and you should not rely on it without further verification and careful adjustment. Always proceed with caution and monitor for detonation (pinging or knocking). Incorrect timing can cause serious engine damage.
