You're tuner should have the 93 tune, is it a 3865?
No you need to run 93 with the 93 tune. I'm just saying if you get caught and only have 91 available and don't want to re tune it will not damage the engine, just drive easier for that tank, don't do WOT runs. Same concept as you can't tow/haul much with the performance tunes, it puts too much load on the engine with that much ignition timing advance. I mean really it doesn't matter because there are knock sensors that retard timing but try to stick with the right octane level. Just when I get caught travelling out of my area and there's no 93, I don't spend 15 minutes at the pump re tuning, I just fill up with the highest grade. Now I probably wouldn't ever put 89 or 87 in the tank with 93 tune, that's a bit of a stretch...
Breathing in and out is good enough for me.