* Engine condition: Worn components, carbon buildup, and other wear will affect optimal timing.
* Fuel type: The type of gasoline used influences combustion.
* Altitude: Higher altitudes require timing adjustments.
* Modifications: Any modifications to the engine (intake, exhaust, etc.) will change the ideal timing.
Instead of a specific number, you should consult your vehicle's owner's manual or a reliable repair manual for the 1991 Chevy Caprice 9C1 with the 305 engine. These manuals will usually provide a *base* timing specification and instructions for verifying and adjusting the timing using a timing light. The process often involves setting the timing at idle, then verifying it under load or at various RPMs.
Without these resources, attempting to find the correct timing is risky and could damage the engine. Improper ignition timing can lead to poor performance, reduced fuel economy, and even catastrophic engine failure.
