Originally Posted by DBH
BMW recommends 93 octane with a minimum fuel grade of 91. They further state "Do not use any gasoline below the specified minimum fuel grade. Otherwise the engine could be damaged.".
Implied here - if the engine is damaged due to low grade (i.e.: 87 octane) fuel, repairs under warrenty may not be covered! With the price difference between 87 and 91/93 you'd have to fill up an awful lot to pay for an new engine!
Just curious...to all of you here who live in 91 octane land, do you really think you are getting the full rated power of this engine? My bet is that you are not. 93 or even 94 octane and cold, dry air at sea level is likely needed for a highly tuned, high revving motor such as this to achieve it's stated power output. I don't know for sure on the M3, but this was definitely the case when I had my RS4.