* Engine modifications: Has the engine been modified (cam, intake, exhaust, etc.)? Modifications significantly affect ignition timing requirements.
* Fuel type: The type of gasoline (regular, mid-grade, premium) influences the optimal timing.
* Altitude: Higher altitudes require different timing than sea level.
* Engine condition: Worn components can necessitate adjustments to timing.
Instead of looking for a specific number, you should consult your owner's manual or a Chevrolet service manual for that specific year and engine. These manuals will usually provide a base timing specification and a procedure for setting the timing using a timing light. They will also often specify how to adjust the timing based on vacuum advance.
Even with the manual, you will likely need to fine-tune the timing. This often involves setting the base timing according to the manual and then testing for optimal performance. This can involve checking the engine's performance (smooth idle, good acceleration, no pinging or knocking) and making small adjustments until the best combination is found. Lack of proper equipment or experience can lead to engine damage.
In short: Don't rely on a single number found online. Find your vehicle's service manual or consult a qualified mechanic for the correct procedure and timing adjustments.
