WJBertrand said:Actually you can. Fuel in Europe is rated by the RON system, as a rule of thumb, take 4 octane points off to get to pump octane number, which is the value our pumps in the US are labeled with. Therefore 95 octane Euro = 91 octane US.
There is still the misconception that higher octane means higher power. This simply not true in the absence of any tuning adjustment. To get the higher octane numbers, alcohol or in the past (MTBE) was added to fuel to slow the burning rate and avoid knock. Since alcohol and MTBE have less energy / gallon than pure gasoline they actually dilute and reduce the total energy in a gallon of premium vs. regular grade fuel. The trade off is that the slower burning fuel will tolerate more aggressive tuning, so the slight loss in available energy is more than made up for by the increased level tune (timing, compression ratio, etc) in a high performance engine. Engines with knock sensing system just automatically adjust the tune, in most cases timing.
My old Honda ST1100 actually started quicker, ran stronger and got better mileage using regular over premium, even at sea level where I live. Of course if I'd heard an knocking I would have switched to premium to stop that happening but at the cost of a slight loss of performance - all engine tuning remaining constant and no knock sensing system.
He said they have 120 RON which would be 115 Octane in the US. Even the race gas here isn't that high.