I love the 'octane' arguments. Well said the post about 89 octane. The 93 octane post reminds me of the story of the little old lady from long ago, that thought she was doing her car good by using high octane when it was designed for 87. In fact it probably was doing harm. Nowadays, with all the sensors (and computer fuel/air adjustments from the mapping tables) you most likely are not doing any damage or having more than a very slight performance degradation (if at all) using 89 octane (don't know about anywhere else but 87, 89, and 93 is available here as a rule). This is given nothing is defective or not nominal within the parts installed. Now, I have a tune, and am not sure if the extended mapping tables for the tune cropped into the memory space in the ECU, or not (if memory capacity wasn't exceeded or if the lower table adjustments were left out/replaced for the extended tables in that tune). This unknown could be hurting my logic about being able to SAFELY use 89 vs 91. My point of view is that if the ECU can adjust two points down from 93, it can adjust two points up from 89 (or vice-versa depending on your point of view). I don't race, or challenge anyone (much) so I just enjoy the less expensive gas. Like I said, I think it is more about preferences and less about damaging this robust motor. This discussion reminds me of another controversy, actually two, the oil filter one and the engine oil one. IMHO