91 Octane in a 340?

I have had a few cars knock on me, if you ever heard a late 90's/early 00's GM start up, they get a knock on the first cylinder to fire almost always, it's that very metallic rattle. Now newer cars with direct injection knock on startup, it's very annoying. Low-speed pre-ignition - Wikipedia
Had a lot of knocking in a Chevy Corvair that I have, especially on hot days.