run 91 minimum.
if you run 87 you'll get slightly less milage per tank. if you run 91 or 93 you'll get slightly more per tank but you'll be paying more.
essentially it's all going to even out so you should run a min of 91 for piece of mind.
hopefully you understand.
the octane booster stuff does nothing and won't help you. the e46 is known to accept 87 however search for "why bmw's require 91 octane" and "pre detonation from lower octane gas" and you'll understand better
Last edited by peytonracer4; 10-25-2012 at 11:53 PM.