Do I need the expensive gas???

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I am pretty new to this "Ultimate Diving Machine" experience. I want to treat my car right, but I also dont want to throw money out the window when I dont need to. My previous cars have never required
premium gasoline, but they have never been BMWs either. I read in the manul to use 91 octane or above to avoid knocking in the engine. But I have also heard reports that unless you are driving a super high performance vehicle that your car wont know the difference between 87, 89, or 93 octance gasoline. I have a 2003 330 CI, It is the most high performance vehicle i have ever owned, but i dont know if it qualifies as needing the higher octane gas...and with the gas prices today, if it doesnt need it, I could save $5-$10 a week by getting the lower gas. What does everyone think? Has anyone had experience with knocking in their engine from lower octane gas?
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91 or 93 octane you now drive a car not only a better vehicle but in order to get better gas mileage and performance and most of all stay away from the shop "dugies25"

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order
I don't belive that he will get any better mileage, nor fewer repairs, by using the correct grade of gas rather than an under-spec rating suchh as 89. Do you have evidence to the contrary? The only problem will be reduced performance.
-Russ.
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Wrong. He will also get less mileage, because the engine computer will have to run the engine richer to keep the intake charge cool. Retarded ignition timing will also result in less mileage, in addition to lower performance.
Floyd
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wrote

Not enrichment of fuel mixture but retardation of spark. Same impact, lower mileage. Whether the reduced mileage (at lower cost per gallon) is less efficient in terms of miles per buck would be an interesting experiment.
R / John
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Somebody wrote:

Russ,
Yes, actually, part of that reduced performance that you mention will be reduced gas mileage. By retarding the spark you will no longer be optimizing the combustion cycle to extract the most power per potential BTU of energy in the gasoline. The potential power in both grades are (roughly) the same, it's the reduced tuning that causes the reduced fuel economy (as well as reduced power output).
As far as the potential for engine damage, if the octane is low enough that the ECU can no longer retard the spark enough to compensate, or if it gets to the point of dieseling, then yes detonation can cause engine damage.
-Fred W
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by
89.
Alright, that makes sense. I wonder if the decreased mileage offsets the increased cost of the gas or not? I found I had better mileage with my chip installed runningg 93 than I did without it on 89, but the cost of premium easily outweighed those savings.

I'm aware of that possibility but I don't think that could happen by running a BMW motor that specs 91 on only 89, do you? Maybe if you lug it up a mountain pulling a trailer...
-Russ.
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The manual says 91 or higher. Use 91 or higher. If the manual is incorrect, you have legal recourse. If you cause damage by using the wrong octane you're on your own.
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You should use 91. You are right, you don't know if it qualifies as needing the higher octane gas. However, luckily for you, BMW does know. They say use 91. If you use lower grades, your car's anti-ping sensors will reduce your engine's performance until the pinging stops, and you will enjoy reduced performance from your machine. Why somebody would spend $30k or $40k on a car and then reduce its performance to save $10 a week, I have no idea.
What the article was *actually* telling you that if you use an octane level in excess of that which is specified, there is no benefit. This is true. 93 octane will not get your car anything extra. 91 octane will not get my car anything extra, because 89 is specified.
You can put a performance chip in your car, or many other cars. Such a chip will modify the engine operating parameters to use the increased anti-ping capabilities of higher rated gas. In that case, you must use the rating indicated by the Chip manufacturer. In your case, a chip might require 93 octane, and to use less would impair performance. Which would negate the reaons for buying the chip in the first place.
-Russ.
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dugies25 wrote:

The owner's manual says: Fuel specifications The engine uses lead-free gasoline only. Required fuel: Premium Unleaded Gasoline, min. 91 AKI. AKI = Anti Knock Index
So the answer is YES, you need to use premium fuel of at least 91 pump octane in the US. If you use less you will get worse fuel economy and run the risk of causing engine damage due to detonation (pinging).
At most stations the added cost of 10 cents per gallon is only about 5% of the cost of the fuel (at ~ $2.00 per gallon). Hardly worth breaking into a sweat about, is it?
-Fred W
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"malt_hound" wrote: > dugies25 wrote: > > I am pretty new to this "Ultimate Diving Machine" > experience. I want > > to treat my car right, but I also dont want to throw money > out the > > window when I dont need to. My previous cars have never > required > > premium gasoline, but they have never been BMWs either. I > read in the > > manul to use 91 octane or above to avoid knocking in the > engine. But I > > have also heard reports that unless you are driving a super > high > > performance vehicle that your car wont know the difference > between > > 87, 89, or 93 octance gasoline. I have a 2003 330 CI, It is > the most > > high performance vehicle i have ever owned, but i dont know > if it > > qualifies as needing the higher octane gas...and with the > gas prices > > today, if it doesnt need it, I could save $5-$10 a week by > getting > > the lower gas. What does everyone think? Has anyone had > experience > > with knocking in their engine from lower octane gas? > > > > The owner's manual says: > Fuel specifications > The engine uses lead-free gasoline only. > Required fuel: > Premium Unleaded Gasoline, > min. 91 AKI. > AKI = Anti Knock Index > > So the answer is YES, you need to use premium fuel of at least > 91 pump > octane in the US. If you use less you will get worse fuel > economy and > run the risk of causing engine damage due to detonation > (pinging). > > At most stations the added cost of 10 cents per gallon is only > about 5% > of the cost of the fuel (at ~ $2.00 per gallon). Hardly worth > breaking > into a sweat about, is it? > > -Fred W
Hey everyone- Thanks...I am sticking with the higher octane, I just wanted hear what others thought. Everyone is correct, saving a few bucks at the pump is not worth ruinning an awesome machine. But at the same time, if the lower octane gas was not helping or hurting, then there is no reason to throw the money away. But since it reduces performance, milage, and could do some long term damage, then it is worth it. Thanks again
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Exactly.
BTW, congrats on your purchase, have fun and visit here more.
Floyd
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dugies25 wrote:

Your engine has a compression ratio over 10:1 - that is definitely high performance land for an engine. It needs 91 octane gas. What many people don't realize is that while the spark is retarded with lower octane gas, it is also very likely that in many situations (pulling a hill, hot summer days, for example) this may not be sufficient, so the next step for the DME is to richen up the mixture. Lower octane and retarded timing tend to increase cylinder head temp - which the DME is monitoring - so it starts throwing in an overly rich mixture to obtain some extra cooling from evaporation of the excess fuel. Now you dump this extra fuel into the catalytic converter - guess what? It starts getting hot. Remember, all this can happen without any knocking. The DME will 'try' to prevent knocking at all cost.
It's all dependent upon driving conditions, load, air temp, etc, but I sure wouldn't do it. Read an article recently (don't remember where) where Steve Dinan went through the intricacies of providing adequate cooling while testing cars on a dynamometer. The M5 he was testing ran the fuel mixture up to as rich as 9 to 1, if I remember correctly, (as opposed to the 'correct' 14 to 1 ratio) during the test trying to keep itself cool - even though he had a pretty good fan blowing air at it to simulate the effect of road speed cooling air flow.
From my own experience, our 91 octane here in CA is such junk that I will often get major brand gas that just doesn't seem up to par. My 328 runs poorly until I drain that tank and fill with another brand. Any trip over to Nevada or Arizona where I clean the tank of CA gas usually gives me better mileage and performance - until I get home.
What would be really neat, and add greatly to these discussions, would be for someone in this group with an OBDII scan tool to run a test using the real-time monitoring capability for spark advance and mixture ratio, using 89 vs 91/93 octane gas. My money's on it showing a quite a difference in 'tough' situations - say pulling up I-15 from Barstow to Vegas on a summer day.
Just my $.02
Frank
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often get major brand gas that just

fill with another brand. Any trip over

better mileage and performance - until I

Ever try a bottle of octane boost when you get a bad tank? If it helps, it's a lot cheaper than a new tank of gas.
-Russ.
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Somebody wrote:

Now that's a good thought. Must admit that my adversion to putting any "mystery" additives into the oil or gas for my cars has prevented this thought from even occuring to me.
Frank
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Raybender wrote:

That and the octane boost stuff costs more than the ~ 10 cents per gallon more that you would pay at the pump for the higher grade fuel in the first place.
-Fred W
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will
thought
Of course, otherwise everybody would just use that instead of buying premium. But, as a spot fix for a bad tank of gas, it's much cheaper than draining and refilling.
-Russ.
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I just don't get it. You have spent a fair amount of dosh on a fairly new car. You have clear instructions from the manufacturer what fuel to use for optimum performance.
For the sake of 500 bucks or maybe a bit more per year you want to consider contravening the instruction?
There is an excellent expression in German: Milchmdchenrechnung (milk maid's calculation).
It just doesn't add up.
DAS
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On Mon, 28 Mar 2005 21:23:18 +0100, "Dori A Schmetterling"

    It's human nature. In Rolls-Royce forums, they have recurring debates on how to use cheaper, non-factory oil filters to save about $20 a year.     Emanuel
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wrote:

You don't get rich by spending money needlessly.
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