or 93? I believe the fuel panel door recommends 87-91, but my state does not provide 91 octane. It jumps from 87 - 89 - 93. I was under the impression that only "Premium" octane gasoline should be used, but wouldn't 89 be considered mid-grade? Would 93 be unnecessary or is it best to use highest octane on a Turbo engine? Should I just stick to mid-grade 89?