You can but that doesn't mean you should. Most cars go into a "limp mode"- they still run, but nowhere near as well as they should. Additionally the most common

You can but that doesn't mean you should. Most cars go into a "limp mode"- they still run, but nowhere near as well as they should. Additionally the most common way to "detect" low octane fuel is with an engine knock sensor, so any engine that tries to optimize itself instead of using a "limp mode" will have to flirt with knock.