If your engine has a knock sensor, and if you don't mind losing some part of
the engine horsepower, then a lower octane rating will be OK.
As for me, I paid a lot of money for the engine horsepower, and I don't like
throwing the power away. So, I use what the manual says.
And, a person who can afford a 740 can afford 91 octane gasoline.
I quite enjoy being able to go from 60 to 120 in a few seconds.
It's not a matter of being able to afford it.
I know European and U.S. gasoline are not formulated the same way. Some
people have suggested that high octane U.S. gas is completely unnecessary
and others have suggested it might even be harmful to the engine. I was
just wondering if anyone here had any facts on the matter.
Higher octane, unless its avgas, isn't going to harm the engine. (This myth
originated from the real truth that higher octane doesn't benefit an engine
not designed to run on it.)
91-93 works great (if you chip the engine, you get a bit of a horsepower
increase with 93 ... may be incompatible with less octane depending on chip
manufacturer). Go to 89 and suffer a slight performance decrease. 87 still
less. The engine will still run okay. I suspect that at $3 a gallon, the
better performance of the higher octane (mileage as well as HP) may be worth
the premium price paid.
R / John
Actually using lower octane gas will hurt the engine over the long run. The
knock is premature ignitioni.e. the ignition is firing before the piston has
reached optimal position. Think of throwing a jab (as in boxing) with the
arm going all the way out. Now throw the jab and jerk the arm back when it
gets 3/4 of the way extended. That is what is happening to your engine on
lower octane. Not only do you lose HP and gas mileage but it has to stress
the engine needlessly.
Is that 91 RON or R+M/2 (European or American)?
My BMW motorcycle also specifies 91 RON as minimum - with about 9% reduced
power from the 98 RON octane recommended. These RON figures, in the US
would translate to about 87 ("regular") and 93 ("premium") R+M/2 or "Pump"
As my lowly '99 328i is designed to run on premium, there's no reason not to
use 93 pump octane in your 740il.
That's pretty much my issue... I don't know. I run 93 octane American in
it... but I'm not sure if that's just above or way above the European
standard BMW is talking about.
I could make the assumption that the owners manual was translated to
American standards since the car was originally sold in America... but
that might be a questionable assumption.
93 octane?! You are lucky! Out here in the San Francisco Bay Area, all
we get is 91 octane, and its not very good.
Some say that if your car doesn't ping or knock, you could run a lower
octane. You probably will lose some power, but if you're in a pinch,
i.e., only regular 85-87oct gas is available, you could use it.
Of course, that presume you haven't modfied your car with a
performance chip. In that case, you need to run only "Super."
Just looked at the manual and my 328i specifies 91 AKI with a minimum of 87
AKI. Wiki defines AKI (Anti-Knock Index) as Pump or R+M/2, so it appears
that BMW has "translated" the octane to US standards. If your manual says
minimum 91 AKI (as does my '03 Z4), then it appears that the knock sensor
can't retard the timing enough to compensate for below 91 octane so you
should probably avoid anything lower. If you can get it, I'd stick with
Of course an exception would be when traveling in high altitude areas where
the octane requirement is lower - I've seen 89 (pump) as premium and have
run it in sensitive vehicles (before knock sensors) with no problems at
about 4,000 feet and above.
Why BMW quotes Euro octane for their bikes and US octane for their cars
makes no sense whatever to me.
E85 is one of the larger hoaxes played upon the population. Significantly
poorer mileage than gas or E10 and no cost savings. Doesn't really do
anything toward energy conservation, independence etc. Drives the price of
other corn products up. A net loss for everybody except the corn/ethanol
production folks and their loyal lapdog politicians.
I live near one of the Ethanol refineries in WI.
They have a factory outlet fueling station that sells
* 89 Octane E10 typically 10 - 15 cents cheaper than everyone else 87 octane
* "Premium" E25 for about 10 - 20 cents cheaper than the E10 and,
* 103 Octane E85 Stays around $2.10 or $2.20 regardless of the price of
If you have a flex fuel engine that can use E85, it can be a good deal even with
the loss in MPG when gas is high, as an added bonus the $$ from E85 mostly stays
I have run E25 in some of my non flex fuel vehicles, there is a small drop in
but less than 5%.
You asked, I replied ...
If you want the advertised power and performance, then use what they say. If
you will take less, then use what you want. If you will take less, why did
you buy what you bought?
The engine will adjust itself to the crap you pour in ...
Put in what they suggest, and drive happy.
On Thu, 10 Jan 2008 18:32:23 +0000, Jeff Strickland wrote:
True... but not in any way helpful or meaningful to the discussion of
fuel in German automobiles.
I thought it was funny.
Had you read the thread you would have found that the discussion was about
the differences between the formulations of American and European fuel as
well as whether BMW was making recommendations based on American or
European standards. Therefore "Put in what they say." is a completely
The discussion of EU vs US was in another subtree, and hence is *NOT*
part of this discussion. If you're reading this with a reader that doesn't
display threads, then you can't keep track of what is meaningful or not.
Jeff makes many factual errors (unintentionally or due to lack of detailed
knowledge), but rarely fails to respond directly to the subject at hand.
I'm sure if you had included a smiley, he would have done better on "dad".
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