Interesting question. My 2021 Kia Soul 2.0 manual says 87 is the minimum octane it should use. So that begs the question “ if i use more than minimum octane, what are the benefits?” Of course there’s no answer, but with gas prices going up with no end in sight the hamster is digesting 87 period. Doesn’t seem to matter either. Just for fun I tried a tank of 91 and found little difference. The engine does have a 12.5:1 compression ratio but it’s an Atkinson cycle mill so what’s the actual comp ratio it’s using at any given time? It’s altered via valve timing but I’ve yet to find out if it’s a fixed valve timing or adjustable, octane dependent. FWIW it never pings that I’ve noticed.