As Hugh mentioned, this is a thread that could go on forever, but as a student of engineering (and I'm sure Dimitrios will back me up here) I wish to correct a possible misconsception. > current engine set up. It seems to me there is no > such thing as premium > fuel. It is all the same stuff, only the plus and > the supreme have > additional additives. The latent power is exactly > the same. the additives > serve to provide a higher resistance to knocking or > pinging and that's it. > I have never heard of detergent in gasoline, but This is not true. Iso-octane is one of two (basic) hydrocarbons that comprise gasoline. In its purest form, gasoline is x parts iso-octane (which is by definition 100 octane) and 1-x parts n-heptane (which by definition is 0 octane). The mixture gives the overall octane rating. Octane is actually calculated empiracly using a standard engine with a variable compression ratio, so that the engine can be adjusted to run without pinging for any octane fuel. Octanes above 100 are possible with different substances such as methyl tert-butyl ether (MTBE), among others. The higher the octane, the greater the power that is available, but, if the engine is not tuned for it, it will be unable to utilize this extra power. Advancing the timing can take advantage of some of this extra power by "fooling" the gasoline into thinking you have increased the compression ratio. But, it only will work up to a point. As for detergents and additives, I have heard that all grades of gasoline from a given manufacturer have the same basic additives and detergents, and really there are only 2 or three producers of gasoline anyway..just lots of different station names! I run 93 octane in my Imperial, with 14 degrees of initial advance, very little vacuum advance, and an average amount of mechanical advance. I also put in a bit of lead substitute from time to time, prolly more for my peace of mind than anything else. But hey, its cheap. ;) ===== --Mike Pittinaro Christmas is over now So I'm changing my haiku Thank you, David Brown __________________________________________________ Do You Yahoo!? Yahoo! Sports - Coverage of the 2002 Olympic Games http://sports.yahoo.com