* Stock 350 with stock compression: Regular unleaded (87 octane) is often sufficient for a completely stock 350 with a stock compression ratio (around 8.5:1 to 9:1). The MSI system helps with combustion efficiency, making lower octane more tolerable than older systems.
* Modified 350: If the engine has been modified with higher compression pistons, a performance camshaft, or other upgrades that increase the compression ratio significantly, it will likely require higher-octane fuel (89, 91, or even 93 octane) to prevent detonation (knocking).
* Best practice: Consult your engine's specifications or a qualified mechanic to determine the appropriate octane for your specific setup. You can also listen for engine pinging or knocking; this indicates detonation and a need for higher-octane fuel.
In short, starting with regular unleaded is a possibility for a completely stock engine, but always prioritize checking your owner's manual or consulting a professional to ensure optimal performance and engine health. Using too low an octane can cause damage over time.
