hi symee,
this is what i get a VW forum which was extracted from one of the brochures on their latest engine(FSI):
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"Thanks to knock control, unleaded four star (at least 95 RON) can be used instead of unleaded Super plus. In order to achieve maximum fuel consumption benefits on the FSI engine, Ultra Low Sulphur Petrol (ULSP) must be used."
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i had the impression that it's better to go for higher RONs(which inturn is better in petrol quality)... no? if i am not mistaken it's the older engines that may have problem if the owner uses higher RONs.
I also have the impression that BHP(horsepower) ratings are not entirely correct due to the RONs. eg. If you use petrol with 100RON, your BHP rating could be higher compare to 95RON.