This is a good topic because Dr. Bill Wattenburg clearly says: "If it isn't pinging, it isn't a problem" in regards to simply using regular gas in any engine. I think he's probably right and I am tempted to step down to the mid-grade at some point just on principle (here we have 87 regular, 89 midgrade and 91 for premium) the reason I haven't tried it yet is if its going to ping it is going to be at the extremes - highway speeds, or in the middle of climbing a hill, or something like that and that may not be a convenient time to switch back to premium.

I will be very interested to see what others have tried. Also, if you have tried regular I hope you will tell us where you are located as altitude is a factor in octane requirements (I am at 3700 ft above sea level - you need less octane at altitude per Dr. Bill - if you don't know who he is just Google).