Last night at a local drive-in car show a person with a lot more experience told me that by mixing 87 & 91 octane gas you would get a higher octane rating than 91. Is this an old wives tale or is there some validity to this claim?
Not true. If you mix them you will end up somewhere in between, depending on the ratio. To get very high octane, you need to mix in something like racing gasoline (there are several web sites with tables that tell you the results for different mixes) or with other chemicals (generally NOT recommended, for reasons too numerous to mention).
In fact, middle grade gasoline is normally just a mixture of high and regular grades.
Now, back in the days o' good old leaded gas, then yes you could do this. The two additive packages had a cumulative effect. But with current fuels it doesn't work.
2 gallons to 20 mix of Toluline (sp) and 92 Octane pump gas will yield you an approximate Octane rating of 94~95. It will not hurt the engine and does not produce any additional pollution. Gas has it in it anyway. However it can get really expensive.
I am sure there are people that don't trust this type mixture but I've ran it and it works and works fine it is just not practical. If your racing then Race Gas can be got at the track in a couple of different flavors, so to speak. If you're street driving then 92 Octane pump gas. Here in Texas our high Octane pump gas is 93.