Thus after you collect a history of good mileage with a good gasoline, you can alter your choice of gasoline to the best one. In my area that one is a Texaco or Shell station. Going to a high octane fuel alone is like going swimming in the Everglades. Chances are, the power will drop off, your engine will run hot and mileage will decay. It seems best efficiency (or optimum pressure point) reached by the engine occurs when the fuel octane is correct. This optimum pressure occurs inside the engine cylinders when the piston is 15 degrees after top dead center. Too high an octane may cause optimum pressure to occur at 25 or 35 degrees after top center which means late timing that causes power to drop and the engine water temp to increase. Too low an octane rating will cause peak pressure to happen at 5 or 10 degrees after top center. Such early timing leads to detonation, loss of power and even engine damage. So you just cannot beat proper timing with proper gasoline by a proper mechanic.