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      11-21-2012, 11:33 AM   #4
Second Lieutenant
NoTempoLimitN54's Avatar

Drives: E92 335i
Join Date: Sep 2012
Location: Los Angeles, CA

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Originally Posted by Sered View Post
Bumping the ethanol content in petrol up will keep the octane the same because they will offset the increased octane from the Ethanol with lower octane petrol; that's the whole point of this I think; they're not simple mixing the existing petrol with pure ethanol.
In the really old days they used tetraethyl lead to increase octane. When that got banned, it was replaced with MMT and later MTBE. MTBE, which was required by the EPA, then gets banned because it leaked out of the underground gas tanks and contaminated groundwater. In 2003, California was the first U.S. state to start replacing MTBE with ethanol.

MMT and MTBE are more effective octane boosters compared to Ethanol. What I don't know is when premium gasoline in CA dropped to 91 AKI. I'm guessing that a reduction in ethanol from 10% to 5.7% might be responsible for the one point drop from 92 to 91. There is a 76 station around the corner from my place, and an old decal on the pump reveals that premium here used to be 92 AKI.

I've got a BMW with two turbos and 10.2:1 compression. I needs me some octane!

For Sale: 2009 335i 6MT (E92/N54), Sport / M-Technic / no iDrive / Black Sapphire / Black Dakota Leather, ZCW, 6FL, PDC, 19" VMR VB3, Pilot Super Sport, M3 control arms + tension links (fr) S. California