Years ago, some of the boosters used an additive that left an orange deposit on plugs and valves. I think this additive was outlawed in the States but I may be confusing it with another octane enhancer that was deemed bad for ground water.
Most of the available boosters will raise the octane only a fraction of an octane number...in other words 93.0 to 93.3.
As Chryco suggested, Av gas will work if you can buy some from a local airport and before someone states that it won't work on the ground because it is blended for high altitude operation, remember that prop planes have to run reliably at low altitude when landing and taking off which is the most critical part of the entire flight. It works quite well when mixed with pump gas.
The other alternative, other than race gas, is to go to the paint store and buy a gallon of Xylene or a gallon of toluene and mix it with about ten gallons of pump gas. Both are aromatics that are commonly mixed into gas to raise octane and anyone that has run race gas will recognize the smell immediately. It is not a bad idea to add an ounce of Marvel Mystery oil to add some lubricant as both are very "dry" compared to normaly gasoline.
If I recall correctly, Xylene is about 117 octane and Toluene is about 114.
