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      11-28-2012, 06:41 PM   #8
Elk
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Drives: 2012 335i
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Quote:
Originally Posted by EB_F30 View Post
Less octane in the fuel is not going to burn as well...more octane equals more power because the fuel is more potent and it's also burning more air...thus making more power.
Higher octane fuels does not contain more energy nor does it require more oxygen for combustion. It merely contains additives that make it less likely to self-detonate.

The only time the use of higher octane fuel results in more power is when an engine is specifically designed for higher octane and, then, only in comparison to when improperly low octane fuel is used in this same engine. As already pointed out above, the use of lower octane in such an engine will pull the timing under some circumstances, reducing power.

The F30 is perfectly happy with 89 octane, as called out in the manual and on the fuel filler door. Some claim 91 produces more power. BMW indicates its power output numbers were produced running 91, but does not state the engines produce more power with 91 nor state that 89 produces less power.

As a practical matter, there will be only a small difference - ~ 3% - if the engine retards the timing on lower octane. This is a difference difficult to detect with a butt dyno.