Minimum octane?

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Hey folks,
I've heard conflicting stories about what gas to put in my car depending on who I talk to.
2000 740il
BMW suggests 91 octane minimum.
Opinions?
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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.
Jim
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On Wed, 09 Jan 2008 13:53:59 -0600, Jim wrote:

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.
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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
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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.
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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" octane.
As my lowly '99 328i is designed to run on premium, there's no reason not to use 93 pump octane in your 740il.
Tom K.
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On Wed, 09 Jan 2008 15:09:08 -0500, Tom K. wrote:

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.

Ah... cool, thanks for the comparison Tom.

Yep... the 740li is a VERY pretty car.
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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."
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On Wed, 09 Jan 2008 14:18:55 -0800, bfd wrote:

Ah... I miss San Francisco, I lived in Santa Cruz for most of my life... though they have taken "progressive" to the point of insanity in the bay area.
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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 93.
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.

Tom K.
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On Wed, 09 Jan 2008 15:09:08 -0500, Tom K. wrote:

Speaking of... any idea where E85 falls in all this? We have a lot of E85 out here in the mid-west.
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Ivan Marsh wrote:

E85 is a VERY BAD IDEA for ANY BMW. The fuel system is not compatible, and a tank might cost you a few thousand $$$ in repairs.
Bad thing that E85.. should feed corn to cows..
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On Wed, 09 Jan 2008 16:55:52 -0500, admin wrote:

Never used it myself but they're really pushing for it... go figure, this is where all the corn is grown.
You can't find gas out here that's not at least 10% ethanol.
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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.
Rant Over, John
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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 E10 (currently $3.00/gal) * "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 gasoline
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 in USA.
I have run E25 in some of my non flex fuel vehicles, there is a small drop in MPG but less than 5%.
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Put in what they suggest.

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On Thu, 10 Jan 2008 17:24:31 +0000, Jeff Strickland wrote:

Yes dad.
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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.
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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 meaningless statement.
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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".
FloydR
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