* Engine size: A 4.3L V6 will have a different timing than a 5.0L V8, and so on.
* Engine condition: Worn components can affect optimal timing.
* Engine modifications: Aftermarket parts or modifications will change the ideal timing.
* Computer control: 1989 Chevy trucks likely have computer-controlled ignition systems. The timing is not a fixed value but is adjusted dynamically by the engine control module (ECM).
You cannot simply look up a single number. To find the correct timing for *your* specific 1989 Chevy truck, you need to consult your vehicle's owner's manual or a repair manual specific to your engine. Even then, the manual will likely give you a *base* timing setting and instructions on how to verify and adjust it using a timing light and possibly a scan tool to monitor the ECM's adjustments.
Improperly setting the ignition timing can cause serious engine damage. If you are not comfortable working on your vehicle's ignition system, take it to a qualified mechanic.
