Octane Booster

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A buddy of mine in work has a Scooby STI and in the never ending quest for improved power and performance has all but decided to add Toluene in measured doses into the fuel tank ie.20% ratio of toluene to petrol in order to boost the octane rating. RON here in Ireland is 95. Much has been read and debated about doing this as he maintains this is a cheaper way of boosting the octane rating,rather than paying through the nose for a bottle of the real stuff in a motor factors.The only thing is he does not know if this will in any way damage the car either in the long or short term.Does anybody have information on this topic or can anybody shed any light on possible problems. Thanks