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      12-13-2011, 09:41 AM   #1
obtix
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Fuel Type

So, while waiting for my X3 I am reading the owners manual. I had originally intended and believed that the car required high octane (91+). Reading the manual suggests 91 or even 89. Oddly, it doesn't say 91 or higher.

So what do you guys recommend and use? When you pull up to the stations with 94 do you use it or stick with 91 (around me, many Sunoco's have 87, 89, 91 and 94)? I also know that octane does not equal performance but the combustion needed for the engine to operate properly.

I got the 28i by the way.
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      12-13-2011, 09:51 AM   #2
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I always go with the highest octane available - even if high octane is not required, it is suggested and the car will lose some performance with lower octane gas....I have the turbo though and always will go for 91+ octane.
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      12-13-2011, 09:53 AM   #3
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Quote:
Originally Posted by fedinand View Post
I always go with the highest octane available - even if high octane is not required, it is suggested and the car will lose some performance with lower octane gas....I have the turbo though and always will go for 91+ octane.
Yeah, due to the compression turbo cars were always like that. My first turbo car was a Volvo 850, burned through gas and oil like you would not believe and needed a min of 91 octane. As much as I wanted the 35i I chose features over engine.

Thanks!
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      12-13-2011, 09:54 AM   #4
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I have the Turbo as well so I stick with 91 or higher.
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      12-13-2011, 09:58 AM   #5
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I have an X3 28i. When I filled up the gas tank today (for the first time!) I noticed the label inside said to use a minimum of 89 octane gas. Do I really need 93, or is 89 adequate?

It seems to me that this should be a binary decision - either the gasoline is high enough to prevent premature combustion, or it's too low and the anti-knock mechanism will need to kick in. Performance should not improve gradually. Am I wrong here?

PB2
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      12-13-2011, 10:02 AM   #6
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Got to agree PB. The knock sensor will just retard timing and in turn reduce performance.

BTW, how do any of us know what is below the pump nozzle? For all we know it's one tank feeding three different pumps.
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      12-13-2011, 10:17 AM   #7
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The old adage question, do you get better gas Mileage with higher or lower octane fuel in the same car?
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      12-13-2011, 10:28 AM   #8
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Quote:
Originally Posted by inamik75 View Post
The old adage question, do you get better gas Mileage with higher or lower octane fuel in the same car?
I don't think it is an age old question. It really what is the car made for and that will give you the best performance and efficiency. To low and to high of an octane will cause many issues.

This always reminds me of when a Turkey Hill opened up near my parents in PA. For opening weekend (years ago) they offered all three grades at $1.00 a gallon. Everyone was in line for 91 octane. I loved seeing the guys with the 89 Chevy filling up with 91.
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      12-13-2011, 10:36 AM   #9
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So I'm still confused - should I put 89 or 93 in my BMW X3 2.8?

The manual recommends AKI 89 or 91. Then it says:

The minimum AKI is 89.

If you use gasoline with this minimum AKI rating, the engine may produce knocking sounds when starting at high outside temperatures. This has no effect on engine life.

Minimum fuel grade. Do not use any gasoline below the minimum specified fuel grade; otherwise engine damage may occur.
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      12-13-2011, 11:25 AM   #10
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Have 35i - I always use 91 but could use 94 as well. Doubt the 94 would make for improved anything, except more dollars to Chevron et al.
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      12-13-2011, 11:32 AM   #11
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89 is the minimum, and 93 is not going to give you anything over 91 other than a bigger fuel bill.
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      12-13-2011, 12:35 PM   #12
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Just use the highest grade you can find.

The difference between the lowest grade and highest is less than $5 each fill up (at least where I live), so the way I see it is if it doesn't do any harm why not use the highest grade since using a lower octane could potentially be bad for the engine.
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      12-13-2011, 01:33 PM   #13
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Quote:
Originally Posted by obtix View Post
So, while waiting for my X3 I am reading the owners manual. I had originally intended and believed that the car required high octane (91+). Reading the manual suggests 91 or even 89. Oddly, it doesn't say 91 or higher.

So what do you guys recommend and use? When you pull up to the stations with 94 do you use it or stick with 91 (around me, many Sunoco's have 87, 89, 91 and 94)? I also know that octane does not equal performance but the combustion needed for the engine to operate properly.

I got the 28i by the way.
The minimum recommended fuel grade is 91, but the tests are done with a higher grade...I think 93 or 97.
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      12-13-2011, 08:00 PM   #14
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I have the X3 28i. For what it is worth I rotate the 89 to 91+ octane. I usely don't let my gas tank get below a 1/2 tank. So one time I will fill it up with 89 then the next time 91 to 93. So you have the happy medium and I don't have any issues runs great.
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      12-13-2011, 09:26 PM   #15
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Actually I found no performance difference between 91 and 89, so just full her up with 89.
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      12-13-2011, 09:51 PM   #16
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Quote:
Originally Posted by fedinand View Post
I always go with the highest octane available - even if high octane is not required, it is suggested and the car will lose some performance with lower octane gas....I have the turbo though and always will go for 91+ octane.
This isn't really true. As long as your engine is not detonating your car will not make any precautionary modifications to your engine controller and your car will behave as designed.

Quote:
Originally Posted by pb2 View Post
I have an X3 28i. When I filled up the gas tank today (for the first time!) I noticed the label inside said to use a minimum of 89 octane gas. Do I really need 93, or is 89 adequate?

It seems to me that this should be a binary decision - either the gasoline is high enough to prevent premature combustion, or it's too low and the anti-knock mechanism will need to kick in. Performance should not improve gradually. Am I wrong here?

PB2
Pretty much, you hit the nail on the head.

Quote:
Originally Posted by lbjgh View Post
Got to agree PB. The knock sensor will just retard timing and in turn reduce performance.

BTW, how do any of us know what is below the pump nozzle? For all we know it's one tank feeding three different pumps.
Normally you have 2 tanks. 1 tank is the lowest grade and 1 one is the highest grade. They mix them together to get the middle grades as it pumps.

Quote:
Originally Posted by inamik75 View Post
The old adage question, do you get better gas Mileage with higher or lower octane fuel in the same car?
Shouldn't be affected as long as you are not detonating.

Quote:
Originally Posted by Beyu View Post
Just use the highest grade you can find.

The difference between the lowest grade and highest is less than $5 each fill up (at least where I live), so the way I see it is if it doesn't do any harm why not use the highest grade since using a lower octane could potentially be bad for the engine.
Waist of $5 a tank!

I would argue that the naturally aspirated BMW engines don't require the high octane fuel they call out. But I wouldn't actually argue not putting in the recommended fuel unless you feel comfortable with the risks.
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      12-14-2011, 12:31 AM   #17
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Less octane will cost you torque and power, plus the engine might not run as smoothly and not as "lively". The higher your altitude, the more you'll feel it.

In Western Europe you fill up with 95/98, so the U.S. 91 is in no way luxurious. And there is no such thing as too high octane in retail fuel. With each ignition the ECU will fine tune the timing, and the better the fuel you feed him the better the engine will run.
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      12-14-2011, 01:13 AM   #18
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Quote:
Originally Posted by RSchneider View Post
Less octane will cost you torque and power, plus the engine might not run as smoothly and not as "lively". The higher your altitude, the more you'll feel it.

In Western Europe you fill up with 95/98, so the U.S. 91 is in no way luxurious. And there is no such thing as too high octane in retail fuel. With each ignition the ECU will fine tune the timing, and the better the fuel you feed him the better the engine will run.
This true have done so on my E60 and forester but consumption wasn't any better sometimes worse on higher octane hence I don't see the point of the extra $$ to get higher octane fuel, if I can get the minimum recommended its what I use.
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      12-14-2011, 02:47 AM   #19
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Quote:
Originally Posted by RSchneider View Post
Less octane will cost you torque and power, plus the engine might not run as smoothly and not as "lively". The higher your altitude, the more you'll feel it.

In Western Europe you fill up with 95/98, so the U.S. 91 is in no way luxurious. And there is no such thing as too high octane in retail fuel. With each ignition the ECU will fine tune the timing, and the better the fuel you feed him the better the engine will run.
This is obnoxious.

The compression ratio of your engine is the ratio of the volume of the cylinder at bottom dead center to the volume of the air at top dead center. Your engine management cannot change the compression ratio to increase the compression ratio (and thus increase power).

When you burn fuel that is too low of an octane rating your engine simply caps the maximum throttle position to reduce the manifold pressure and reduce the chances of detonation.

You CANNOT improve fuel efficiency or power with a higher than required octane ratio.

Formula 1 cars don't use a very high octane fuel (relatively speaking). This is because they are running at such high rev's the fuel cannot detonate (not enough activation time) even though the temperature is high enough. It does not affect their power output.
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      12-14-2011, 03:00 AM   #20
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Quote:
Originally Posted by paul386 View Post
This is obnoxious.

The compression ratio of your engine is the ratio of the volume of the cylinder at bottom dead center to the volume of the air at top dead center. Your engine management cannot change the compression ratio to increase the compression ratio (and thus increase power).

When you burn fuel that is too low of an octane rating your engine simply caps the maximum throttle position to reduce the manifold pressure and reduce the chances of detonation.

You CANNOT improve fuel efficiency or power with a higher than required octane ratio.

Formula 1 cars don't use a very high octane fuel (relatively speaking). This is because they are running at such high rev's the fuel cannot detonate (not enough activation time) even though the temperature is high enough. It does not affect their power output.
maybe you can explain why the car feel smoother and nippier on higher octane, ie engine response is faster on same pedal acceleration this for me is when i put Shell V-power higher octane fuel.

Last edited by Bimar; 12-14-2011 at 03:11 AM..
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      12-14-2011, 03:04 AM   #21
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Quote:
Originally Posted by paul386 View Post
This is obnoxious.

The compression ratio of your engine is the ratio of the volume of the cylinder at bottom dead center to the volume of the air at top dead center. Your engine management cannot change the compression ratio to increase the compression ratio (and thus increase power).

When you burn fuel that is too low of an octane rating your engine simply caps the maximum throttle position to reduce the manifold pressure and reduce the chances of detonation.

You CANNOT improve fuel efficiency or power with a higher than required octane ratio.

Formula 1 cars don't use a very high octane fuel (relatively speaking). This is because they are running at such high rev's the fuel cannot detonate (not enough activation time) even though the temperature is high enough. It does not affect their power output.
Please!

Ignition timing of course influences engine output. And that's where the benefit of higher octance numbers come into play.

And who has been talking about compression ratio??
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      12-14-2011, 03:16 AM   #22
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Quote:
Originally Posted by inamik75 View Post
maybe you can explain why the car feel smoother and nippier on higher octane, ie engine response is faster on same pedal acceleration this for me is when i put shell V=power higher octane fuel.
For the same reason so many people on these forums think they have dynamic dampers and they really don't.

The energy released by your gasoline can be very easily modeled with a simple thermodynamic process and a stoichiometric chemistry balance. In no way does the octane rating of the fuel affect either of these properties.

Can you explain to me the properties that a higher octane rated fuel adds to the equation that allows it to generate more power?

Quote:
Originally Posted by RSchneider View Post
Please!

Ignition timing of course influences engine output. And that's where the benefit of higher octance numbers come into play.

And who has been talking about compression ratio??
Higher compression ratio and higher intake air temperature are the properties of a turbo'ed engine that cause them to require higher octane fuel. Not their ignition timing.

Yes a car retards the ignition with fuel that is too low of an octane rating. But if you fuel has a sufficient octane rating that detonation does not occur than your timing is not retarded and further increasing octane is not beneficial.
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