Well, yes, there is a reason why race cars use super high octane gasoline..... they're very high compression, and lower grade gasoline can ignite via compression before the spark plug fires, causing knock (and possible damage over time). The higher the octane, slower the fuel ignites. The Acura has knock sensors that will change the timing once it 'senses' that the octane is lower than expected....thus a possible loss of power, and a potential loss of mileage. Damage to the engine? Apparently not, according to the Acura mechanic. That said, I decided not to try regular, or Ethanol for that matter, even though Ethanol is available around here at 90 octane. Honda obviously engineered the 3.5 to use premium.... believe I'll stick with it. Anyway, if there really is a drop in HP and mileage, it will erode the savings over time.