[Bob Parmenter]

Hey Doug,

The difference between "winter" gasoline and "summer" gasoline is Reid Vapor Pressure. Winter gasoline has more "light ends"(of the distillation range) that will vaporize more readily for lower temperature starting. This should have virtually no effect on octane rating.

I'm not familiar with the term "logy" so I have no idea what you mean by that, but octane rating (e.g. 91 or 93) has to do with whether or not your engine knocks(or pings if you prefer that terminology). If nothing has changed in your tune up, and your engine doesn't ping, then higher octane alone won't do anything to improve anything. You can potentially get more performance from a higher octane fuel if you change your tune up to take advantage of the higher octane rating (more resistance to knock). Generally that means changing timing.

Fact of the matter is, knock should be less of an issue in lower temperature months since you are getting a denser charge and lower cylinder temperatures with the cooler air. Knock (and the operational knock level) is basically a function of temperature all other conditions being equal.

Mixing leaded fuel with a premium unleaded fuel will result in a higher octane, but the effect will vary depending on mixing ratio, and lead volume. My guess would be, even in a racing fuel, the lead content today is pretty light, which would mean only marginal improvement. But again, if you don't have knock on the unleaded premium, then you're just spendin' money. If you do change your tuneup to take advantage of the octane boost, and the perceived improvement is worth it to you, then spend away.............it's your dough.