You wont notice any difference unless your cars are at the top end of tuning and have turbo chargers fitted. Optimax - 98 Ron BP Ultimate - 97.1 to about 97.5 RON (they *wont* gaurentee the rating ... make your own mind up) Other SUL - 97 RON UL - 95 RON You only really need the higher octaine rating if you are suffering from pre-detination (knock). An n/a engine is unlikely to generate enough pressure/heat to cause this. If you have a TMO/Pocketlogger/Other software monitoring device then please post up some figures. It will be easy to tell if the car performs any better from this. I would sa