gas and octane question

If you`re not running a ton of advance and super high compression then run the lowest octane you can without detonation. Start with a mid grade gasoline, say 89 octane. Drive the car in a high gear at a slow speed and mash the gas without downshifting. Listen for what sounds like all of your valves rattling. If you don`t hear it then your 89 octane should be okay, if you hear a rattle then move up to 91 or 93 octane. Your car will tell you what it needs, you just have to listen.