[mcbrew]

If your engine is knocking, you'll get a CEL. Unless that is happening, there should be no benefit to premium gas in our engines. "Butt dynos" are not very well calibrated. Your car might "feel" different with premium gas, but I doubt there is more power. There is no reason there should be more power. There is a good reason there should be less power: there are fewer BTUs per gallon in premium than in regular. By a very small amount, though... probably less than most people could detect.

Running premium will not hurt your engine... it just won't have any benefits, all else being equal. There is a catch there... because all else might not be equal. There may be other additives in the premium, or it may be a different brand than you usually use. I suspect that it is mostly a placebo effect. If anyone has dyne numbers that show otherwise, I will listen.

The same thing happens with biodiesel vs. regular diesel. Biodiesel has a lower BTU content. A given engine will have lower fuel economy and lower power on biodiesel, but many people report having more power. The reason is mainly that biodiesel makes the engine run quieter, so it seems like it isn't working as hard. The difference is small... but lower BTU content equals lower power. This is the same reason that E85 returns much lower fuel economy than regular gasoline or E10. Ethanol has a much lower BTU content than gasoline.