different alcohols
Isopropyl alcohol does not behave like methanol or ethanol. At that higher alcohol percentage you were in effect increasing your fueling and reducing your WI cooling. Same thing happened to WWII fighter aircraft. When they substituted Isopropyl alcohol for methanol or ethanol without changing injection amounts they blew up engines.
Isopropyl alcohol in high concentrations acts more like a fuel than a coolant.
I suspect if you go to the 90% concentration you would need to change your injection rates, or increase your water percentage, to maintain knock resistance. High concentrations of some alcohols have been rumored to be sensitive to pre-ignition as well.
You get maximum cooling effect with 100% water. You need to add some alcohol to compensate for the dropped combustion temperatures. It takes somewhere between 10% and 50% methanol or ethanol to get max power depending on fueling and ignition settings.
Larry
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