Autozone is now stocking VP Madditive OCTANIUM . It adds upto 8 full numbers to 10ga of gas. I just do half of this mix with 90 octane ethenol free gas to get a 94 rating. Have also ran the full 98 a few times. Cannot say I notice a big difference in power but does run smoother.
Also like to add a gallon of VP110 leaded to a full tank every now and then. Good for your engine but ruff on the o2 sensor.