if you dont want your baby to cough, you better give her the good stuff 91+ I can only get 93 here in New york.

 

Shell 91, otherwise the car feel lack of power.

 

I recall reading some BMW information stating that the ECU is programmed for the lowest commonly available unleaded premium fuel where the car is sold. In the US, it happens to be 91 octane (R+M/2 method), although many regions of the country have 93 octane available.

That being said, the engine management systems on all BMWs (and other premium vehicles) have built-in anti-knock sensors and programming so that if you use lower octane rated gasoline, the engine will not be damaged by knocking (or pre-ignition of the fuel). Thus, I do not believe that the use of lower octane gasoline will damage your high compression engine due to the knocking.

However, you will experience lower engine performance (since the ECU is tuned for the higher octane gasoline). In addition, some brands of gasoline have additional detergent additives for their premium unleaded fuels that are apparently not included in their lower octane gasolines => if true (and not just a marketing gimmick), then it is preferable to use the higher octane fuel because it is cleaner than lower octane fuels and will not foul up your engine internals.

I have also heard that many people who lease vehicles, but do not intend to buy them, often use lower octane gasoline than recommended by the manufacturer. If true, then caveat emptor to any later buyer of such "pre-owned" vehicles.

 

I think most cars (or at least those I have owned) can retard the timing when lower grade fuel is used (provided is within the range). Loss of power is definitely there.