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Old 01-24-2012, 09:55 AM
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SteVTEC SteVTEC is offline
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Mein Auto: '11 E93 / '12 E70d
Originally Posted by nhs156 View Post
Your manual should be specific about whether 93 is "recommended" or "required" - there's a crucial difference. For the vast majority of cars these days, onboard electronics are programmed to compensate for lower octane fuel, technically making 93 octane obsolete for all but the highest end of sports cars. Various tests by car mags and consumer organizations have confirmed that lower octane fuel has no/neglible adverse effects (performance, wear, emissions or mpg) on the vast majority of new cars.

That said, I could've sworn I felt a slight performance difference when using 89 and 91 fuel in my wife's Audi (a 3L supercharged engine with 333hp). It was ever so slight, but I could've sworn I felt a tiny difference. That combined with unfounded doubt in my mind, made me switch back to 93. I figured the marginal incremental cost annually of 89 vs 91 vs 93 didn't warrant the lower grade fuel. I only use 93 in the M5, but would be comfortable with lower octane fuel in a non-M BMW if BMW only "recommends" 93.
This is true, but premium luxury/sports car engines are not "most vehicles", and thus the difference you think you felt in your supercharged Audi, which was most likely real and not placebo effect. I wouldn't put anything less than 91 in a turbocharged BMW either. And as more and more smaller displacement forced-induction engines come out in 'normal' cars, I wouldn't be surprised if this rule of thumb starts to change either.
2012 E70 X5d (IT'S HERE!) Deep Sea Blue / Sand Beige, Premium, 3rd Row, Multi-Contour
2011 E93 335i Deep Sea Blue / Oyster, Step, Premium, Convenience (PDC & CA), and that's it

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