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BMW 3-Series and 4-Series Forum (F30 / F32) | F30POST > Technical Forums > N20, N26, B46, B48 Turbo Engine / Drivetrain / Exhaust Modifications > What octane do you put in your 328i?
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View Poll Results: What octane do you put in your 328i?
87 octane 2 2.25%
89 octane 15 16.85%
91 octane 72 80.90%
Voters: 89. You may not vote on this poll

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      08-14-2012, 01:08 PM   #1
Mahzari
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What octane do you put in your 328i?

The gas cap says 89, but out of habit I've been putting 91 in my car.

What octane do you guys put in your 328i? What's your thinking one way or another?
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      08-14-2012, 04:19 PM   #2
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We only have 95 and 98.. Mostly i use 98
Switzerland
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      08-14-2012, 04:25 PM   #3
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Quote:
Originally Posted by kruemel View Post
We only have 95 and 98.. Mostly i use 98
Switzerland
Different countries use different measurements. For reference, your 95 octane (measured in RON) is roughly equal to our 91 octane (measured in AKI). 98 RON is approximately 93 AKI.
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      08-14-2012, 04:31 PM   #4
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Ah ok thanks for the info
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      08-15-2012, 04:48 PM   #5
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In the UK BMW use 98 RON fuel when they quote the power output of the car. Therefore that's what we need to use for best performance / economy. I presume it's the same elsewhere.

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      08-15-2012, 04:53 PM   #6
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98 RON here in Australia as well. Been putting it in my E90 since day 1 and will continue with F30 when it arrives. Like in the UK, performance figures here are based on 98RON fuel, but BMW's recommendation is for 95RON even though the car will adapt to fuel between 91RON and 98RON.
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      08-15-2012, 11:36 PM   #7
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Thanks for all the replies. Sounds like I'm going to keep putting in 91 octane.
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      08-16-2012, 05:22 PM   #8
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It's a 4 cylinder. I think I'll add the 89 if that is a BMW recommendation.
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      08-16-2012, 07:30 PM   #9
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Higher octane is generally more important for forced induction motors, such as the F30. Seems factory tune is to 89 and it probably would not make much of a difference, but I will stick with 91
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      08-16-2012, 09:08 PM   #10
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American fuel for as bad as you think the quality may be, is actually decent enough. The manufacturers design the cars to be driven with near sludge for fuel so they have knock sensors that help all types of climates (hot mostly) to ensure that the cars can still "run" but they will not be at their best because the knock sensor primarily removes timing from the car.

That being said, I run 91 because I would like all 240hp available to me if the need comes up. I would put 85 in the car and feel fine if that was all the gas station had though.
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      08-27-2012, 07:44 PM   #11
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I just put a tank of 89 in... 100 miles in and it feels the exact same. Haven't done any comparisons to see if it's slower or not, though.
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      08-28-2012, 12:48 PM   #12
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My Saturn SKY recommends 87, but the Turbo model recommends 91. Since I have forced induction on a 10.4:1 compression ratio engine I run Tier 1 91. I also run 91 in the 328i for basically the same reasons.
While not every computer is the same, the general principal of one Bosch ECU vs another is going to generally be the same. In the case of the ECU used in the Turbo Sky (and my SKY for that matter) there are 2 ignition timing tables among other tables that all have a multiplier for octane rating. Based on knock under specific conditions the engine will modify that octane rating and effectively change the 'tune' of the engine. If it's really bad you will eventually fall all on the low octane timing map and even when you do put better fuel in it may take a bit for it to adjust back to the higher octane.

Without having extensive access to many details of the BMW ECU (Like I do with the SKY) it is all but impossible to know exactly how the engine is responding to the fuel being delivered, but for the most part just monitoring knock counts can help establish what works best for a given engine. The difference on the extents are so small that it would be almost impossible for a butt dyno to tell the difference and only with some telemetry could you really tell.
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      08-29-2012, 02:39 PM   #13
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You should add a 93 octane option for the Northeast!
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      08-29-2012, 07:31 PM   #14
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Quote:
Originally Posted by Rich@GTBPerformance View Post
You should add a 93 octane option for the Northeast!
I was thinking about a 91+ option, but I can't change a poll after it's published
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      08-29-2012, 08:00 PM   #15
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Quote:
Originally Posted by Mahzari View Post
I was thinking about a 91+ option, but I can't change a poll after it's published
No problem. I feel for you guys in Cali. Wish you could have 93 octane out there.

I'd have to get my Gas imported if I moved GTB there
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      08-29-2012, 11:18 PM   #16
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Quote:
Originally Posted by Rich@GTBPerformance View Post
No problem. I feel for you guys in Cali. Wish you could have 93 octane out there.

I'd have to get my Gas imported if I moved GTB there
I wish we did, too.

The only consolation is that there is a station about 10 minutes from my house that sells 91 octane (regular price), 95 octane ($6.99/gallon), and 100 octane ($8.99/gallon). So if I ever get a UGR Gallardo I'll be able to fill it up... For about $200
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      08-30-2012, 07:29 AM   #17
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Quote:
Originally Posted by Mahzari View Post
I wish we did, too.

The only consolation is that there is a station about 10 minutes from my house that sells 91 octane (regular price), 95 octane ($6.99/gallon), and 100 octane ($8.99/gallon). So if I ever get a UGR Gallardo I'll be able to fill it up... For about $200
LOL

If you have a UGR Gallardo, $200 will be less than the bottle of wine you'd drink with your Kobe Beef Ribeye every night of the week

Oh man, now I am making myself hungry.
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      08-30-2012, 12:18 PM   #18
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Quote:
Originally Posted by Rich@GTBPerformance View Post
LOL

If you have a UGR Gallardo, $200 will be less than the bottle of wine you'd drink with your Kobe Beef Ribeye every night of the week

Oh man, now I am making myself hungry.
You don't need to be *THAT* rich to buy a UGR Gallardo. You can also pick up an early Gallardo for $80,000-100,000 and spend another $40,000 to make it insane. One forum over and there are people paying $110,000 for a brand new M5, and don't even get me started on M6 pricing.

Then again, spending $140k on your second car must mean you're pretty well off.
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      08-31-2012, 08:40 AM   #19
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For n/a motors i use 87. However for forced induction motors i use a good 91 octane. 76 and chevron are my preferences. Sunoco if i can find it. Learned it from my evo before where i experienced knocking on cheap gas. How much more if RON was lower. The f30 is a very quiet car so i wont probably even hear anything. I have yet to even hear the turbo
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      08-31-2012, 05:47 PM   #20
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Quote:
Originally Posted by rexg View Post
For n/a motors i use 87. However for forced induction motors i use a good 91 octane. 76 and chevron are my preferences. Sunoco if i can find it. Learned it from my evo before where i experienced knocking on cheap gas. How much more if RON was lower. The f30 is a very quiet car so i wont probably even hear anything. I have yet to even hear the turbo
Have you floored it yet? The turbo is fairly loud at full tilt, but there's little to no blow off noise
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      09-01-2012, 07:33 AM   #21
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Run 91 Octane

On the four cylinder the manual said you could use 89, but when you do, it may throws a code to the computer that the turbo is running lean. It doesn't hurt the engine. But you may have problems down the line. For a few cents more a gallon run 91.
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      09-01-2012, 12:34 PM   #22
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Quote:
Originally Posted by RWS-F30 View Post
On the four cylinder the manual said you could use 89, but when you do, it may throws a code to the computer that the turbo is running lean. It doesn't hurt the engine. But you may have problems down the line. For a few cents more a gallon run 91.
No... If the manual (and gas cap) says it, then BMW intended the car to run that way. It would only run lean if: the car said 91 and I put anything less or my car was tuned and I continued to put 89. Do you listen to the manual when it says what oil to put it? If so, why no listen to it when it says what gas to put in?

Full tank of 89 gone and it drives exactly the same as 91 octane. I think people are just experiencing the placebo effect. Every body that's been in my car hasn't noticed or commented on any difference. Even after I tell him it's on 89, they say it feels just as fast.
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