* Year of manufacture: Pontiac 389s were produced across many years, and factory specifications varied.
* Engine modifications: Cam shaft type, compression ratio, carburetor setup (single vs. dual, type of carb), and the presence of any performance modifications (headers, etc.) all significantly affect ideal timing.
* Fuel type: The octane rating of the fuel influences ignition timing. Higher octane allows for more advanced timing.
* Engine condition: Wear and tear can affect optimal timing.
Therefore, you cannot simply look up a single number.
To find the correct ignition timing for *your* specific 389:
1. Consult a factory service manual: This is the best source. Find a manual specific to the year and model of your Pontiac. It will provide the base timing specification and instructions on how to adjust it.
2. Use a timing light: After setting the base timing as per the manual, you may need to fine-tune it using a timing light. This involves adjusting the distributor while observing the timing marks on the engine's harmonic balancer. You'll likely want to do this while the engine is running. Many resources online show how to use a timing light.
3. Consider a professional tune-up: If you're unsure about performing this yourself, a mechanic specializing in classic cars or Pontiacs can accurately determine and set the optimal ignition timing for your engine.
In short: Don't guess. Use your car's specific service manual or consult a professional. Attempting to guess the timing can lead to engine damage.
