What octane fuel should I use?

[tranquility]

I know I should use at least 91 but when I was at the pump I saw that there was also a 94 grade...would it make any difference if I pumped 94 or even higher? Thx.

[Dr Stig 2]

BMWs come fitted with knock sensors.
That means you can put in fuel between 91 and 98 octane
(NOTE: unless they do something silly in the states to stop people litigating for having too much power and potentially hurting themselves by spilling hot coffee while accelerating )

The higher octane you use, the slightly higher power you will get out.
Top Gear did a dyno test on an Evo a few years back to show the difference in power output.

Over here, they recommend 95 as a minimum, but preferably 98 with the 35is, but you can use down to 91 octane on occassions if we have to (when we cant find any of the good stuff).

Its in your manual.

[teagueAMX]

Originally Posted by tranquility

I know I should use at least 91 but when I was at the pump I saw that there was also a 94 grade...would it make any difference if I pumped 94 or even higher? Thx.

Octane is a combustion inhibitor. With respect to internal combustion engines, it's basically an indication of a fuel's ability to resist pre-detonation. In regular terms it means that in a high compression engine it allows better ignition timing which translates to more horsepower.

So to answer your question, it's better if you use a higher octane fuel, and as Dr Stig 2 mentioned above, BMW has sensors on the engine that modify the engines settings when you use lower octane fuel.

Edit: The n54's static compression ratio is 10.2:1, which is fairly high by today's standards. The only way that can be maintained is through computer control. However, in the turbocharged engine the dynamic compression ratio will increase dramatically due to forced induction. This reaffirms the need for a higher octane fuel to allow the engine to maintain the high potential horsepower under all circumstances.

[MDLFCS]

Here in Alaska, the highest octane available as premium unleaded is 90. I wonder if I need an octane booster.

[teagueAMX]

Octane booster can be beneficial, but running it all the time will be expensive.

Cooler weather in Alaska can help the engine, so I'd save it for warmer weather when you want to take it out for a good run.

[KrisNL]

Some info on Octane and listed per country.

http://en.wikipedia.org/wiki/Octane_rating

[teagueAMX]

Originally Posted by KrisNL

Some info on Octane and listed per country.

http://en.wikipedia.org/wiki/Octane_rating

Great link. Interesting point here:

Wikipedia - Octane rating
Octane rating does not relate to the energy content of the fuel (see heating value). It is only a measure of the fuel's tendency to burn in a controlled manner, rather than exploding in an uncontrolled manner. Where octane is raised by blending in ethanol, energy content per volume is reduced.

That's what they are doing to our fuel, making it less efficient, and there is no evidence that pollution derived from organic blending will be better for us in the long run.

[tranquility]

Right now I've only seen 91 and 94 as the higher grades at the pumps. So it is better to go w/ the 94 in all cases? My manual does not state much save for 89 being the absolute min and 91 being the recommended.

[mcbeee]

Originally Posted by tranquility

Right now I've only seen 91 and 94 as the higher grades at the pumps. So it is better to go w/ the 94 in all cases? My manual does not state much save for 89 being the absolute min and 91 being the recommended.

In Canada (and you are) 91 is the normal "premium" but with the ethanol blends available 94 octane is available. I use Husky/Mohawk 94 octane almost always. It has less than 10% ethanol, it will give better performance but does not give better fuel economy than the normal 91 octane. That is why Husky/Mohawk dropped one grade from the pumps and charge the same for their 94 as others do for 91.

[cdeslandes]

In North America, use 91 octane. Your engine is designed to work with 91 octane, so you will not gain any noticeable power from using a higher octane rating, but would lose power if you use a lower rating as your ECU adjusts timing to avoid knocking and save your engine from damage.

The only exception would be on very hot days (above 90F/32C) when even 91 octane would barely keep the engine from knocking and 93/94 would be preferrable.

Note that 91 is about as high an octane rating as one can find on the US West Coast, while in the East 91 is hard to find so get 93 instead.

Also note that:

89 (US/Canada) = 95 (Europe)
93 (US/Canada) = 98 (Europe)

give or take a point.

[tranquility]

Originally Posted by cdeslandes

In North America, use 91 octane. Your engine is designed to work with 91 octane, so you will not gain any noticeable power from using a higher octane rating, but would lose power if you use a lower rating as your ECU adjusts timing to avoid knocking and save your engine from damage.

The only exception would be on very hot days (above 90F/32C) when even 91 octane would barely keep the engine from knocking and 93/94 would be preferrable.

Note that 91 is about as high an octane rating as one can find on the US West Coast, while in the East 91 is hard to find so get 93 instead.

Also note that:

89 (US/Canada) = 95 (Europe)
93 (US/Canada) = 98 (Europe)

give or take a point.

Thx, that's clear enough. However, I'm confused about your bolded part though. Why don't the pwrs that be keep things standardized?

[teagueAMX]

They are different standards of measurement that developed independently in different parts of the world at different times. I'm sure different scientists and engineers have their favorites.

Nobody want's to say, "OK, I give up and we'll use your system."

[tranquility]

Originally Posted by teagueAMX

They are different standards of measurement that developed independently in different parts of the world at different times. I'm sure different scientists and engineers have their favorites.

Nobody want's to say, "OK, I give up and we'll use your system."

Is there any topic you don't know something about? You are the MAN, the Lion King lol.

[teagueAMX]

As the Bicentennial Man says, "One is happy to be of service".

Thanks for the generous compliment.

[cdeslandes]

Originally Posted by tranquility

Thx, that's clear enough. However, I'm confused about your bolded part though. Why don't the pwrs that be keep things standardized?

The powers that be are not the same on different continents

There are two ways to measure octane, that yield indices about 10 points apart. In the American we use the average of the two, in Europe the highest of the two.

So for a given brand of gasoline:

RON = 85
MON = 95

European rating (MON) = 95
US/Canada rating (AKI) = (85+95)/2 = 90


To confuse things further, the US and Europe use different horsepower definitions.

So my Z4 makes 300 hp in the US on 93 octane, and would make 306 hp on 98 octane if I took it back to Europe!

[juhap]

Originally Posted by teagueAMX

Nobody want's to say, "OK, I give up and we'll use your system."

Although I wish they would sometimes. Some systems are clearly better than others.

[tranquility]

Originally Posted by cdeslandes

The powers that be are not the same on different continents

There are two ways to measure octane, that yield indices about 10 points apart. In the American we use the average of the two, in Europe the highest of the two.

So for a given brand of gasoline:

RON = 85
MON = 95

European rating (MON) = 95
US/Canada rating (AKI) = (85+95)/2 = 90


To confuse things further, the US and Europe use different horsepower definitions.

So my Z4 makes 300 hp in the US on 93 octane, and would make 306 hp on 98 octane if I took it back to Europe!

I'll just take your word for it and use 91 from now on (Canada rating), lest my head explodes thinking more on this topic lol.

[teagueAMX]

Originally Posted by tranquility

. . .lest my head explodes thinking more on this topic lol.

Heads exploding is not good - please don't.

[teagueAMX]

Originally Posted by juhap

Although I wish they would sometimes. Some systems are clearly better than others.

+1

[mcbeee]

Let's get North America to use one system of measurement for distance first....miles or Kilometers....we'll tackle the rest later....I think the US and the UK are the only places that still use miles

I still do fuel usage in MPG's .... WTF, I'm old so I'm allowed...

[teagueAMX]

I'm ready for full on metric change over. Fought it back in the '70s and '80s when the US started talking about converting, but then had to learn it anyway. Now, I look back and don't know why I didn't want to migrate to metric because it's so easy. Just haven't memorized all the conversion factors.

[Dr Stig 2]

Originally Posted by teagueAMX

I'm ready for full on metric change over. Fought it back in the '70s and '80s when the US started talking about converting, but then had to learn it anyway. Now, I look back and don't know why I didn't want to migrate to metric because it's so easy. Just haven't memorized all the conversion factors.

There was a Wizard of Id cartoon once on conversion...

King: We are going metric, under pain of death
Rodney (to crowd): Anyone who doesn't go metric will be beaten within an inch of their lives...
Silent frame: (Rodney upside down in chains in dungeon)