* Engine condition: Worn parts, carbon buildup, and valve adjustments all affect optimal timing.
* Fuel: The octane rating of the fuel significantly impacts detonation risk and thus timing.
* Altitude: Higher altitudes require adjustments to ignition timing.
* Modifications: Any modifications to the engine (camshaft, heads, intake, etc.) will drastically change the ideal timing.
* Load: Timing often varies depending on engine load (idle, cruising, WOT).
Instead of a single number, you need to consult the owner's manual or a reputable workshop manual specific to your 1970 Plymouth 440 375 HP engine. These manuals will provide the *base* timing specification, often at idle. Even then, you'll likely need to fine-tune the timing using a timing light and following the procedure outlined in the manual. This often involves checking timing at different RPMs and loads.
Without this documentation, providing a specific timing number would be irresponsible and potentially damaging to your engine. Incorrect timing can lead to poor performance, reduced fuel economy, or even engine damage.
