* Engine condition: Worn components, carbon buildup, and other issues will affect the ideal timing.
* Fuel type: The octane rating of the gasoline influences how much advance is safe.
* Altitude: Higher altitudes require less advance.
* Modifications: Any modifications to the engine (camshaft, intake, exhaust, etc.) will significantly alter the ideal timing.
Instead of a specific number, you should consult your owner's manual. It will likely specify a base timing value. However, even this base timing may need adjustment based on the factors listed above.
The best way to find the optimal timing is through a process called "timing the engine." This typically involves:
1. Setting the base timing: This is usually done with a timing light, connecting it to the #1 cylinder spark plug wire and aligning the timing mark on the crankshaft pulley with the indicator mark on the timing cover. The owner's manual, or a repair manual specific to your vehicle, will show you how to do this.
2. Tuning the timing: Once the base timing is set, you'll likely need to adjust it slightly for best performance and efficiency. This can be done by adjusting the distributor. You would look for peak performance (highest RPM at wide-open throttle and/or best fuel economy), and might need a vacuum gauge for more refined tuning.
In short: Don't rely on a single number found online. Find your owner's manual for the starting point and then use a timing light and potentially other diagnostic tools to fine-tune the timing for your specific engine's condition and your location. A repair manual specific to your truck will also be very helpful.
