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E90/E91/E92/E93 (2006 - 2013)
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  #1  
Old 03-04-2011, 06:22 AM
S4RIN S4RIN is offline
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Why your 3 series needs 91+ Octane Fuel

Premium Fuel Article

Better mileage, Better performance, More Power.

“Pretty much consistently amongst all the tests – which cover vehicles from 20 years old up to brand new – generally speaking you have an 8 to 10 per cent improvement in power on any car,” - Quote from Article.

So next time you'll think twice before reaching for that regular.
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  #2  
Old 03-04-2011, 06:45 AM
Ounce Ounce is offline
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I've never understood why this is an even argument for a car like this. If the price of premium gas is too much for someone who can buy a $35K+ car then you might want to check your budgeting priorities

Interesting test and results, it is definitely good to know that you're getting what you pay for in this situation. Out here we only have 93, which I imagine is even better than the 91 only available in certain areas.
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  #3  
Old 03-04-2011, 06:52 AM
Michael Schott Michael Schott is offline
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Nothing new in this article. We know that performance and fuel economy suffer when we use gas with lower than recommended octane. The question is by how much. A tuner in this article says as much as 8-10% which I think is BS. I try to use only 93 in my 328 (91 is hard to find where I live) but when I've used 89 or even 87 no way did I feel that I'd lost about 20 horsepower. And most admittedly anecdotal reports say 2-3%.
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Old 03-04-2011, 06:59 AM
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German owner's manual states the following:
  • 98 RON for advertised performance.
  • 95 RON can also be used, minimum for the N54 engine.
  • 91 RON minimum.
  • Diesels: fuel in according with DIN EN590 (cetane of 49)

AKI is 3-4 points lower than the RON scale. American fuel quality sucks, so BMW NA just asks 91 AKI for safety's sake.
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  #5  
Old 03-04-2011, 07:09 AM
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Originally Posted by Ounce View Post
I've never understood why this is an even argument for a car like this. If the price of premium gas is too much for someone who can buy a $35K+ car then you might want to check your budgeting priorities
+1

Even if 87 is $3.55 and 93 is $3.75, what's 20 cents when gas is already almost 4 bucks?
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  #6  
Old 03-04-2011, 07:15 AM
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Compression ratio > 9.5:1 generally does far better with higher octane fuel. Isn't the N54/N55 like 10.2:1?
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  #7  
Old 03-04-2011, 07:41 AM
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Any article that shows real data tends to show that using higher octane than recommended is not beneficial. But I agree the story is more complicated when engines wear out and lose compression. I don't think I've seen data for those scenarios.

BTW, why do people care what others put in their tanks?
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Old 03-04-2011, 08:01 AM
Tom K. Tom K. is offline
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Originally Posted by E92Submarine View Post
+1

Even if 87 is $3.55 and 93 is $3.75, what's 20 cents when gas is already almost 4 bucks?
It's about 5.6%, and if there really is a 5% fuel economy gain (although I'd like to see some more studies - especially using BMWs), then 93 is a no brainer.

But when the differential gets is closer to 10% (i.e. 87 at 3.50 and 93 at 3.85, which is not uncommon), then I tend to alternate tanks of 87 & 93.

Turbo owners have a different scenario as 89 is BMW's stated the minimum.

And regarding high compression motors needing 93, my BMW motorcycle with 12:1 compression will run smoothly on 87 in a pinch, albeit at reduced power and economy. (BMW quotes an 8% reduction in peak power for that motor.)

Tom
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Old 03-04-2011, 08:59 AM
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Quote:
Originally Posted by thekurgan View Post
Compression ratio > 9.5:1 generally does far better with higher octane fuel. Isn't the N54/N55 like 10.2:1?
This is the main reason for the need of 91 octane. The improved fuel economy and performance is a desired side-effect.

If the company that makes the engine and has no interest really in what gas you buy and where tells you what type of gas to buy, why wouldn't you? Do those people also buy light bulbs with sockets that don't mach their lamps and try to cram them in there anyway?
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Old 03-04-2011, 10:00 AM
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Originally Posted by cwinter View Post
This is the main reason for the need of 91 octane. The improved fuel economy and performance is a desired side-effect.

If the company that makes the engine and has no interest really in what gas you buy and where tells you what type of gas to buy, why wouldn't you? Do those people also buy light bulbs with sockets that don't mach their lamps and try to cram them in there anyway?
Because BMW doesn't tell you to buy 91 (at least for the N52). BMW tells you that 91 is RECOMMENDED for maximum performance and fuel economy, but that 87 and 89 are fine.

I would also point out that there the familiar YMMV really holds here. No two of us are in the exact same driving conditions, atmosphere, etc. So, what is true for one of us may not be true for a second.

I've run 87, 89, and 91 in my car. And, regardless of what any tests suggest, I think the loss of performance with 87 is quite noticeable. I see a major improvement from 87 to 89. From 89 to 91, I feel little difference at all. This is all at LA atmospheric conditions.

In terms of MPG, I've assessed this very carefully and found no difference at all from 87 to 91. Its basically unchanged. So, count me as a unbeliever on this topic.

Now, all that said, I have never put anything in my car other than 91 after that initial exploration. Honestly, I don't see the sense in spending $40,000+ on a car and then decrementing my enjoyment of it just to save $150 a year.
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  #11  
Old 03-04-2011, 04:44 PM
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Quote:
Originally Posted by Kilgore Trout View Post
Because BMW doesn't tell you to buy 91 (at least for the N52). BMW tells you that 91 is RECOMMENDED for maximum performance and fuel economy, but that 87 and 89 are fine.

I would also point out that there the familiar YMMV really holds here. No two of us are in the exact same driving conditions, atmosphere, etc. So, what is true for one of us may not be true for a second.

I've run 87, 89, and 91 in my car. And, regardless of what any tests suggest, I think the loss of performance with 87 is quite noticeable. I see a major improvement from 87 to 89. From 89 to 91, I feel little difference at all. This is all at LA atmospheric conditions.

.
I've also experimented with mid-grade and premium on the 325i (N52) and found that the only discernible difference would be at full-throttle, higher-rpm (a bit less max hp). Fuel consumption remains the same and there's no difference in throttle response. So I usually just do mid-grade or premium depending on the price differential (which can be steep in VA)
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  #12  
Old 03-04-2011, 04:54 PM
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Quote:
Originally Posted by Ounce View Post
I've never understood why this is an even argument for a car like this. If the price of premium gas is too much for someone who can buy a $35K+ car then you might want to check your budgeting priorities

Interesting test and results, it is definitely good to know that you're getting what you pay for in this situation. Out here we only have 93, which I imagine is even better than the 91 only available in certain areas.
I completely agree with everything you said... never a question to use anything but premium, but you have to admit it bums you out when gas is $4.12/gallon (like it is in California right now) no matter what your budget is...
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Old 03-04-2011, 05:01 PM
rictor20 rictor20 is offline
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It depends on the compression ratio in your engine. Higher compression engines do need the higher octane fuel to prevent a condition call pre-ignition, most people call it spark knock or ratteling. The truth is that all three levels of fuel are the same. The higher octane Premium Gas is exactly the same as the low octane Regular gas. It just has an additive which causes it to be less volatile. Here's how you can tell if you need (Premium). Next time you need gas, fill your tank with regular. If you hear your engine pinging or making a small ratteling noise, just go to an auto parts store and get some octane booster and add it to your tank. If you don't hear anything like that, Your auto will be just fine on regular gas. This is what causes pre-ignition. The air fuel mixture is compressed in the cylinder. Compression causes heat. Low octane fuels in a high compression engine will actually ignite due to the compression before the spark plug fires. When that happens you hear the knock or ratteling. Pre-ignition or pre-detonation, as some people call it can damage your pistons. Try the low octane (regular gas), If you engine runs quietly, Your good to go. Hope this helps.
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  #14  
Old 03-04-2011, 05:55 PM
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Quote:
Originally Posted by Kilgore Trout View Post
Because BMW doesn't tell you to buy 91 (at least for the N52). BMW tells you that 91 is RECOMMENDED for maximum performance and fuel economy, but that 87 and 89 are fine.
In terms of MPG, I've assessed this very carefully and found no difference at all from 87 to 91. Its basically unchanged. So, count me as a unbeliever on this topic.
Now, all that said, I have never put anything in my car other than 91 after that initial exploration. Honestly, I don't see the sense in spending $40,000+ on a car and then decrementing my enjoyment of it just to save $150 a year.
I've been running 87 since mid-January. Avg. 22.5 combined & 30 hwy. No difference. My E91 runs the same as it did w/91. As we get into hot weather & pinging becomes an issue I'll jump to 89 or 91 if I feel the car needs it. It isn't an issue of money. The car simply runs fine on 87. I only use Shell & buy at the same station 90% of the time.
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  #15  
Old 03-04-2011, 06:32 PM
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I know lots of people say 87 doesn't degrade performance, and it could all be a placebo effect. But, I think the drop in performance is very noticeable. Personally, I'm sticking with 91.
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Old 03-04-2011, 06:35 PM
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Kilgore just posted that using premium costs him maybe $150 more per year. I figure it costs me about $200/year. More or less 50 cents per day to do what's recommended. 'Hardly seems like a big deal.
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Old 03-04-2011, 07:46 PM
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Quote:
Originally Posted by Kilgore Trout View Post
I know lots of people say 87 doesn't degrade performance, and it could all be a placebo effect. But, I think the drop in performance is very noticeable. Personally, I'm sticking with 91.
Agree. It's just not worth it for the joy of driving, which is why we buy BMWs for in the first place ......................... right????
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Old 03-04-2011, 07:59 PM
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Originally Posted by rictor20 View Post
It depends on the compression ratio in your engine. Higher compression engines do need the higher octane fuel to prevent a condition call pre-ignition, most people call it spark knock or ratteling. The truth is that all three levels of fuel are the same. The higher octane Premium Gas is exactly the same as the low octane Regular gas. It just has an additive which causes it to be less volatile. Here's how you can tell if you need (Premium). Next time you need gas, fill your tank with regular. If you hear your engine pinging or making a small ratteling noise, just go to an auto parts store and get some octane booster and add it to your tank. If you don't hear anything like that, Your auto will be just fine on regular gas. This is what causes pre-ignition. The air fuel mixture is compressed in the cylinder. Compression causes heat. Low octane fuels in a high compression engine will actually ignite due to the compression before the spark plug fires. When that happens you hear the knock or ratteling. Pre-ignition or pre-detonation, as some people call it can damage your pistons. Try the low octane (regular gas), If you engine runs quietly, Your good to go. Hope this helps.
Rictor, your summation is correct but your conclusion is misleading. Modern engines have knock detectors* which sense preignition and report it to the ECU. When the signal reaches the preprogrammed threshold the ECU retards (ignition) timing so that the burn begins later in the piston stroke.

This ability is what enables a high compression, high performance engine to run smoothly on a range of octanes. However, the conclusion cannot then be made that just because the ECU adapts timing to suit octane that any octane is fine. Sure, low octane won't knock because the timing is backed way off, but performance will suffer as a consequence.

High octane fuel will resist preignition, a phenomenon which results in the mixture exploding before the piston is in optimum position to maximize energy absorption. Significantly, higher octane also results in a more controlled flame propogation which, in layman's terms, results in a push of the piston rather than a punch to the piston.

If an engine is designed to maximize the potential of high octane gas, then the engine will be most efficient if it is run on high octane gas.

*Used to be actual piezoelectric devices bolted to the head(s) which sensed shock waves and generated a signal. In the late 90's some brilliant Bosch engineer figured out a way to impute knock by analyzing the rate of ionization across the sparkplug tip in each cylinder. That's how the best engines do it now, and Bosch gets a royalty on every system.

Last edited by DSXMachina; 03-04-2011 at 08:10 PM.
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Old 03-04-2011, 08:05 PM
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Agree. It's just not worth it for the joy of driving, which is why we buy BMWs for in the first place ......................... right????
I bought mine for the status. I don't drive it. I back it into the garage and leave the door open so that my neighbors in their Camrys can't miss it when they drive by. I sit in a lawn chair out front and wave to them in a slightly distracted manner. Kill.
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Old 03-05-2011, 02:37 AM
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I bought mine for the status. I don't drive it. I back it into the garage and leave the door open so that my neighbors in their Camrys can't miss it when they drive by. I sit on a couch that's on the roof of my raised ranch with a Bud heavy and wave to them in a slightly distracted manner. Kill.
You are from NH. Fixed.
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Old 03-05-2011, 03:17 AM
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I bought mine for the status. I don't drive it. I back it into the garage and leave the door open so that my neighbors in their Camrys can't miss it when they drive by. I sit in a lawn chair out front and wave to them in a slightly distracted manner. Kill.
I wish that this Message Board had a Rep button, I would definitely add it if I could.
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Old 03-05-2011, 05:13 AM
todd92 todd92 is offline
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You lose a little bit of power (certainly not 10%) and depending on your driving style, you may not even notice it. MPG is hardly effected at all. To the extent that MPG might be effected, remember, that if you get worse MPG, then the higher the price goes, the LESS sense it makes to try to save $0.20 cpg by switching. The same goes for driving out of your wat to go to a cheaper station. Do the math.
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Old 03-05-2011, 05:58 AM
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If you have to worry about the price of fuel in a german luxury performance vehicle, your a penny pincher that does not understand the relationship between quality, and value.
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Old 03-05-2011, 07:09 AM
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I bought mine for the status. I don't drive it. I back it into the garage and leave the door open so that my neighbors in their Camrys can't miss it when they drive by. I sit in a lawn chair out front and wave to them in a slightly distracted manner. Kill.
Then again, at least according to some on the board, our E90s are no more than the functional and status equivalent of a Camry anyway.
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Old 03-05-2011, 10:39 AM
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..which are debadged Lexus's anyway...pffftf!
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