I've been doing this for years. Just so happened to stumble across a good write-up on it.

Enjoy;)

http://www.elektro.com/~audi/audi/toluene.html

I've used Toluene a lot of times with great results, I mix a toluene gallon with maybe 15 lts of gas, no knocks nor pings and great performance, I love race gas though, but toluene it's a great when u are shot or money for buying race fuel.