Yes, this is a high compression, high performance engine. If you do not use the proper fuel, it will damage the engine, but what does this really mean??? Well, instead of getting say 250,000 miles out of your car, it might quite at 200,000 miles. It's not a big difference but just the same you bought this car for high performance so put in the matching fuel.That's if you ALWAYS use regular gas, the 4 past fill ups aren't going to make much of a difference... perhaps it cost you 1,000 miles but who cares, you will sell this car before it dies. Don't be concerned with the past, press the gas and GO!OMG, there are lots of people here that don't know the long term effects. Sure there's a knock sensor on ALL cars that will retard the timing, but why should the engine knock at all in the first place if you are using the correct fuel? That little bit of knocking before the computer compensates for stupid people that think computers are smart will indeed cause the engine to wear (just a tiny bit) faster than normal. The real impressive thing about gasoline engines is not how they work, but how they work for so many miles!