I'm halfway through my first tankful and my fuel mileage is the same as it was on premium (93 in NC). My tank still had about 3 gallons of premium in it when I filed with regular, and for the first little while I felt no change in performance. Now that I'm about halfway through the tankful, I think I can detect a decrease in performance. It's not huge and it only appears to be the case at light throttle openings and high rpm. Flooring it seems to deliver pretty much the same response (and sweet sound) up to 6,000 rpm.

Since the difference in price is more than 10%, I'm inclined to keep using regular.

Don't have mine yet but good to know. I'm not afraid of trying this myself (although I'll probably go middle of the road and use 89). Please keep us posted.

Ben

I never said I couldn't. As I said in my post though, I am just experimenting to see what difference it really makes. I expected to see a much bigger difference than I have so far. Quite a surprise actually. I expected a big drop in all round performance and that I would want to switch back immediately to premium. As for the car deserving premium, do you really think so? If running regular makes litle to no difference in real world driving, then why pay the oil barons more than you have to?

Once again, it's just an experiment.

Latest results are a trip to VIR to see the AMA Superbikes this past weekend. Mostly highway, but with stop lights etc. Averaged 18mpg on regular. Performance was all there when I wanted it. Now I have to run a couple more tankfuls before I switch back to premium. Then I'll let you all know if I feel a boost in performance or not.

It appears to be supported by the physics of the internal combustion engine. So obviously, the knock sensors are supposed to retard the ignition to eliminate knock. They appear to work well, as I detect no knock. The question is, how much difference does it really make under normal driving conditions? How frequently does the ignition actually get retarded to avoid knock, and under what conditions? Well so far it appears that it happens very infrequently in my driving, and it's bloody hot around here right now which I thought might make for worst case conditions. I'm sure if the engine were being constantly lugged up hills in a high gear with the throttle floored (conditions usually used to successfully find knock in an engine if there is any) then maybe the performance drop-off would be more significant. Maybe also if I was blasting around at 6,800 rpm everywhere too. Since neither of these conditions are true for me, I guess that's why I see such a small difference.

In any case, I'll revert to premium soon just because. But is is interesting to note that the same 10% level of savings can only be achieved through fuel economy measures if I absolutely baby the throttle everywhere and annoy everybody behind me by accelerating so slowly.

Interesting experiment that's almost over. In the end I'll put premium in it and wax it with the most expensive wax just because I can.