* Engine condition: Worn components, carbon buildup, and valve train issues will all affect optimal timing.
* Fuel quality: Lower-octane fuel requires less aggressive timing to prevent detonation.
* Modifications: Any modifications to the intake, exhaust, camshaft, or other engine components will drastically alter the ideal timing.
* Altitude: Higher altitudes require different timing settings.
Factory Recommendation: The factory service manual will give a *starting point* for the base timing. This is usually around 10-12 degrees BTDC (Before Top Dead Center) at idle. However, this is just a starting point for initial adjustment.
Finding the Optimal Timing: The best way to determine the optimal timing for *your* specific IROC-Z is through:
* A timing light: This allows you to measure the actual timing.
* A vacuum gauge: This helps assess engine vacuum which is an indicator of engine health and can help you fine-tune timing.
* Careful observation: Look for signs of detonation (pinging, knocking) which indicate the timing is too advanced.
* A dynamometer (dyno): The most accurate way to find optimal timing is by using a dyno and systematically adjusting the timing to find the highest horsepower and torque output.
In short: Don't rely on a single number. Start with the factory recommendation (around 10-12 degrees BTDC) and use a timing light and vacuum gauge to fine-tune for best performance and to avoid engine damage. If you are not comfortable working on your engine's ignition system, it's best to consult a qualified mechanic.
