I have an '01 LS. As others have noted, the owner's manual RECOMMENDS premium. It is not REQUIRED. There may be reduced performance with lower octanes. The Mazda VVTi, like the Porsche, Varioram, varies timing on the intake side only. The BMW Double VANOS varies timing on both intake and exhaust. Neil Tusing Dual Citizenship: Del-Val/LVMOC