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Message: <blockquote data-quote="rpmnut" data-source="post: 487916" data-attributes="member: 20757">Most BMW's are optimized for RON 91 - RON 98 petrols. If you're not sure what your car is tuned for, check the fuel flap. The sticker on the back of the flap will tell you what's the minimum RON your car needs to run. But do note - the lower the octane, the lower the power your engine will produce. Lower octane petrol has lower knock-resisting properties, so to counteract this, the engine ECU on knock-sensor equipped cars (all BMW engines have this), will retard ignition when it detects auto-ignition (heard as mild "knocking" or "pinging" noises from the engine when under load), resulting in some power loss in the interest of engine longevity.</blockquote>