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Yes. You should use what the mfg suggests, because that's what the electronic control module is programmed to get peak efficiency from. However, your ECM will retard your timing to keep you safe from knock/detonation if you use a lower grade. However, retarded timing will show a noticeable drag on power. The inverse isn't true, b/c the ECM is programmed for 91 octane gas (E36, at least), and will not advance timing to get any real power gain from a 93 or higher octane gas. Note: do not use diesel, leaded gas, or anything but your usual, unleaded pump gas.