I recognize that more octane does not equal more power, but would adding something more flammable, like xylene, increase the explosive-ness of the gas, increasing power?
A higher octane fuel "slows" the speed of the explosion of the fuel, and lowers the heat in the chamber. If you are in great tune and drive "normally" you should be fine. I have seen many burnt exhaust valves on teardown of earlier engines, and wouldn't take the chance myself.
lower quailty fuel evaporates fast than high quailty fuel . thus when you let your car sit for a while after running it the fuel evaporates from the carb making it harder to start.
If you were to magically get 150 octane, odds are it woudln't run in an 8:1 engine. Octane is not power, octane is how high the compression can get before pre-detonation. If you don't have the compression for higher octane, you gain nothing. In Texas, I doubt you'll get the chance, but run 93 octane on a cold day. It takes the car twice as long to get to a steady idle as it does with 87 octane. On days below 30*F, my 74 Comet would barely start with 93, once it didn't. Try bumping your timing until it pings on 87. If it doesn't ping before you get into the 30's initial timing, 38* total, there is no benefit to higher octane.
I don't think this is an octane issue. Has more to do with the evaporation temperatures of the blend of gasoline. Here in Wisconsin, summer blend boiling points are around 400 degrees and winter blends are around 100 degrees. All has to do with converting the liquid gasoline into a combustable fuel/air mixture inside the carburator venturi vacuum. Summer gasolines, if used in cold weather will cause hard starting and rough idle until the engine warms up enough to help the fuel mix at the right ratio (about 16:1 in our cars) and burn using the cold air. Opposite is true if winter blends are used in hot temperatures, you can get a vapor lock. In Texas, your blend swings are not as severe as they are in the colder climates. But a high boiling point summer blend will not run good in cold weather. I'd be willing to bet that the higher octane fuel you had was a high evaporation summer blend and that caused the poor cold starting condition. Eric J
