That is interesting, and nice to know. I will have to say that my car has run really great every time I've put Shell premium into it. Not sure if the extra octane make the difference or not. If so, then I'm sort of hesitant to run less than 91 in mine. Had an 88 truck a number of years ago that was supposedly tuned to run on 89 octane, but, ran like crap on anything less than 91. Seems there is definitely a difference in fuels between octane ratings.