Oh man... very :thumbsdown: :thumbsdown: :thumbsdown: Now I'll have to think twice before justifying a M5. :)

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To the best of my knowledge, BMW does not adjust the timing based o the region. New engines will automatically adjust to prevent knock and damage, and there will be less than optimal performance.
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Correct, the timing will be retarded until the 'knock threshold' is achieved. BMW has an 'ionic current sensor' that they use to detect the onset of knock. The car will automatically adjust each individual cylinder's spark timing such that the timing is advanced to the maximum level that does not result in knock. With 91 octane gas, there will be some adjustment of the spark timing, and the resultant loss of power. A 10-12 HP loss certainly sounds reasonable, and if it's cold out you may not see any loss at all. Remember, this drop in HP is not going to be perceptable to the average person. 10-12 HP equates to about 100 lbs of weight. That's the difference in performance between a car with a full and a quarter full tank of gas.

If you're really concerned, you could use some of the high quality additives to increase the octane.

Got it.
Thanks, and by the way, your car will be in your hands in a few days now...is there a pump near you that sells octane >91 or do you intend on supplementing the fuel with an octane boost?

One of the benefits of living in Ohio - 94 octane fuel available at the Sunoco stations. There's one about a mile away from my house.

One of the benefits of living in Ohio - 94 octane fuel available at the Sunoco stations. There's one about a mile away from my house.
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You lucky bastard. :thumbsup: :P