High-octane fuel largely a waste of time

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wrote:


Maybe this is why my highway mileage is better then rated by BMW. I used 92-93 octane (US rating) and on long trips averaging about 75mph I get about 37 mpg. Normally about 22 in town.
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Thanks, Fred, I learned something here. The great thing about standards is that there are so many to choose from!
My car, the '92 525i Touring, says in the accompanying manual and in my aftermarket (Delius Klasing) manual that the M50 motor needs fuel with an RON of 95 or an AKI of 90. I'll have to look closely the next time I'm at the pump, but here in British Columbia, Canada, I believe they rate the fuel in AKI.
So, in short, I'm buying premium gas. I would think my best bet is to buy 91 most, if not all, of the time (assuming I always top up a tank that's half full or so). If 89 is of a high enough quality, I would be happy to learn why.
-- Mike
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snipped-for-privacy@gmail.com wrote:

You are correct AKI is the same as PON. RON+MON/2.
If the minimum recomended is 90, you would have to get 91 to be absolutely certain you are "in spec", but many manufacturers state they recomend one grade buit the car will tolerate a much lower one.
YMMV, as they say... ;-)
--
-Fred W

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For those of you (in the US) that are members of BMWCCA, Mike Miller had things to say about this subject in techtalk in this month's magazine: "use premium if the manual calls for it."
FloydR
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