[kokopuffs405]

93

[RPM90]

Originally Posted by Mahzari

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.

No placebo. It's based on science and physics.

BMW doesn't "recommend" 89 US octane fuel.
That is a minimum recommended octane rating, meaning the engine will run ok with that fuel grade. You can even run 87 octane in your turbo, the knock sensors will trigger and the ECU will alter tuning to compensate.
The best performance required rating is 91. Will 93 be better? That depends on whether the engine is tuned to achieve higher output that requires 93.
The one benefit to using 93 is that it gives a greater "head room" to knock occurring in the first place. You may not get more power with 93, but it could help reduce the tendency for knock.

The reason the engine can run that lower octane is because the engines have a knock sensor. With 87 or 89 octane the engine will fun just fine...until it encounters knock, which it will once you start increasing throttle input along with higher temps. Then, the ECU will start to retard timing until those knock events get under control. When timing gets retarded so does peak power production and efficiency.

As you continue to drive the ECU will continue to advance timing again to get back to peak efficiency. If you're driving moderately, and the air temps are not too hot you can keep knock at bay for a while, until it rears it's head again. Then, the ECU will retard timing again to get it back under control, and the cycle repeats.
The point is that the ECU will keep trying to get back to best efficiency and best power output, but if you don't give it the required fuel, then it can't get there and stay there.

You may not notice a difference for a couple of reasons.
One, the engine will run smoothly and fine even though it may be producing less power.
If you're just driving around in daily driving and not using a lot of throttle, you'll likely not notice the reduced power, as you're not asking for more power.
Knock tends to occur at high loads and greater throttle with high compression loads.
Another reason could be that you're used to the reduced power so you don't notice it's gone.

Still, the fact is that these turbocharged engines with rather high compression ratio's for turbo engines, REQUIRE higher octane fuel to run at their best.
That can be measured on a dyno, no placebo recommended or required.

There is a big misconception about octane. There are a good number of people who believe that their engines will perform better and give them more power, and even better MPG, simply by running high octane "premium" fuel. No, that not true. If an engine is designed to achieve it's peak power and best efficiency on 87 octane fuel, then running 91 or 93 octane will NOT give them more power nor better fuel economy. Those people are throwing their money away for no reason, other than their misunderstanding of fuel octane and their engines.
That is not the case here with BMW's turbo engines, and high performance NA engines.

There are many places on the web to get this kind of info.
Here is one in particular that cites BMW and GM engineers.
http://forum.roadfly.com/threads/126...ctane-gasoline

[Mahzari]

Originally Posted by RPM90

No placebo. It's based on science and physics.

BMW doesn't "recommend" 89 US octane fuel.
That is a minimum recommended octane rating, meaning the engine will run ok with that fuel grade. You can even run 87 octane in your turbo, the knock sensors will trigger and the ECU will alter tuning to compensate.
The best performance required rating is 91. Will 93 be better? That depends on whether the engine is tuned to achieve higher output that requires 93.
The one benefit to using 93 is that it gives a greater "head room" to knock occurring in the first place. You may not get more power with 93, but it could help reduce the tendency for knock.

The reason the engine can run that lower octane is because the engines have a knock sensor. With 87 or 89 octane the engine will fun just fine...until it encounters knock, which it will once you start increasing throttle input along with higher temps. Then, the ECU will start to retard timing until those knock events get under control. When timing gets retarded so does peak power production and efficiency.

As you continue to drive the ECU will continue to advance timing again to get back to peak efficiency. If you're driving moderately, and the air temps are not too hot you can keep knock at bay for a while, until it rears it's head again. Then, the ECU will retard timing again to get it back under control, and the cycle repeats.
The point is that the ECU will keep trying to get back to best efficiency and best power output, but if you don't give it the required fuel, then it can't get there and stay there.

You may not notice a difference for a couple of reasons.
One, the engine will run smoothly and fine even though it may be producing less power.
If you're just driving around in daily driving and not using a lot of throttle, you'll likely not notice the reduced power, as you're not asking for more power.
Knock tends to occur at high loads and greater throttle with high compression loads.
Another reason could be that you're used to the reduced power so you don't notice it's gone.

Still, the fact is that these turbocharged engines with rather high compression ratio's for turbo engines, REQUIRE higher octane fuel to run at their best.
That can be measured on a dyno, no placebo recommended or required.

There is a big misconception about octane. There are a good number of people who believe that their engines will perform better and give them more power, and even better MPG, simply by running high octane "premium" fuel. No, that not true. If an engine is designed to achieve it's peak power and best efficiency on 87 octane fuel, then running 91 or 93 octane will NOT give them more power nor better fuel economy. Those people are throwing their money away for no reason, other than their misunderstanding of fuel octane and their engines.
That is not the case here with BMW's turbo engines, and high performance NA engines.

There are many places on the web to get this kind of info.
Here is one in particular that cites BMW and GM engineers.
http://forum.roadfly.com/threads/126...ctane-gasoline

I completely agree with the bolded part, but I'm not sure where BMW has ever mentioned that the N20 needs 91 octane to reach the quoted 240hp / 260lb/ft of torque. The manual mentions that 89 is the minimum but has no mention of higher octane levels.

That being said, if I were to pick up a tune and run 91 octane, I'm sure I'd pick up a considerable amount of power.

[Maz335i]

So,

For a 335i, considering its and i6, should we use 91 or 93?

I mostly go with 91 but at times kinda get stuck with 89...

What's the best recommendation for a 335i?

[Mahzari]

Originally Posted by Maz335i

So,

For a 335i, considering its and i6, should we use 91 or 93?

I mostly go with 91 but at times kinda get stuck with 89...

What's the best recommendation for a 335i?

BMW recommends 91 octane for the 335i. Going above the recommended will not be beneficial, but I would not make a habit of going under either.

[Maz335i]

Originally Posted by Mahzari

BMW recommends 91 octane for the 335i. Going above the recommended will not be beneficial, but I would not make a habit of going under either.

Thanks bud!

I noticed a serious dip in my MPG everytime I use 89, so I guess I'll go back to 91...

[friederbluemle]

Thanks for the info RPM90!
I use 91 octane gas.

[justinnum1]

93

[Maz335i]

Originally Posted by justinnum1

93

Yeh, used 94 today.

[elistan]

Originally Posted by Mahzari

I completely agree with the bolded part, but I'm not sure where BMW has ever mentioned that the N20 needs 91 octane to reach the quoted 240hp / 260lb/ft of torque. The manual mentions that 89 is the minimum but has no mention of higher octane levels.

That being said, if I were to pick up a tune and run 91 octane, I'm sure I'd pick up a considerable amount of power.

Page 303 of the owner's manual.

[AWMSPORT]

Always used. 93. Will neverchange. (unless Need it badly and out of 93. Then just enuf to get me to another station . ) lol

[kppanic]

Originally Posted by Maz335i

Yeh, used 94 today.

Petrocan 94? I heard Shell vpower 91 > petro 94 due to the fact that shell having 0 alcohol.

[Mahzari]

Yesterday I filled up with 91 octane and I haven't really noticed any difference. I want to see if the cold start and idle will be quicker with 91 octane in addition to be faster.

But BMW using 91 octane for the dyno testing was news for me. Thanks for sharing the info.

[Mrcarcrazy]

Originally Posted by Mahzari

Yesterday I filled up with 91 octane and I haven't really noticed any difference. I want to see if the cold start and idle will be quicker with 91 octane in addition to be faster.

But BMW using 91 octane for the dyno testing was news for me. Thanks for sharing the info.

Gas in Cali sucks anyway, so may not help much. But using simple science you can easily prove that an engine designed to run on 91 prefers to run on 91. (this is an oversimplification, it's friday....I'm not wasting an hour typing up what you can read in a book)

[Sock_Puppet]

Originally Posted by RPM90

No placebo. It's based on science and physics.
...
There are many places on the web to get this kind of info.
Here is one in particular that cites BMW and GM engineers.
http://forum.roadfly.com/threads/126...ctane-gasoline

Thanks for the info, RPM, that was a good read.

[Sauveur]

91

[Mahzari]

Originally Posted by Mrcarcrazy

Gas in Cali sucks anyway, so may not help much. But using simple science you can easily prove that an engine designed to run on 91 prefers to run on 91. (this is an oversimplification, it's friday....I'm not wasting an hour typing up what you can read in a book)

I understand that, that's why a 335i runs terribly on 89 octane. What throws me off is that the gas cap says 89 is the minimum for the 328i (where as it says 91 is the minimum for the 335i). I guess you guys were right saying that "minimum" is not the same as "preferred."

I'm half way through my tank of 91 and I do have to say that cold starts are quieter and it idles more smoothly... Maybe I'm converted back to using 91 octane permanently

[M.Suka]

93 always!

[Mrcarcrazy]

Originally Posted by Mahzari

I guess you guys were right saying that "minimum" is not the same as "preferred."

Precisely.

[hotsoup]

I'd fill up on 89 but Costco only carries 87 or 93 :/

[edgarik]

A full tank will cost an extra $1.50 for 91, I highly doubt $6 a month will impact anything

[bnekic]

93 only