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Old 02-08-2014, 08:32 AM
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Why is premium gas recommended in a 320i?

This thread isn't the many about which gas is better or if one should use premium.

The topic is why the 320i recommends premium gas. For the 328i, I can see. Hypothetically, maybe the 328i produces 240 hp with 93 octane and 231 with 89. These figures are made up. If so, why wouldn't BMW just make a 320i that produces 180 hp with 87 octane?

FYI, my paperwork says the car has 181 hp but the sales literature says 180. The owners manual states that premium is recommended but doesn't specify which octane. It states that 89 is required. The fuel filler door states 91 is recommended, 89 required. In Vancouver, 94 is sold. I haven't used it yet since it's more than $2/gallon more than 92 just across the US Canadian border.

Last edited by Dave 20T; 02-08-2014 at 08:33 AM.
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Old 02-08-2014, 09:30 AM
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Let us know if you notice slower performance with regular gas on 320i.
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Old 02-08-2014, 09:36 AM
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I put premium in all my car, required or not.


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Old 02-08-2014, 10:42 AM
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I suspect it's to combat premature detonation or "ping." As with all turbo cars, the effective compression is much higher leading to higher chance of pre-ignition. The cooling effects of direct fuel injection helps to alleviate this (hence the high 10:1 compression ratio), but the higher octane of premium will help more. The lower octane rating is a minimum, beyond which I suspect the computer's timing parameters may not be able to compensate.
Premium fuels also usually have higher levels of detegents, but whether that will do any good when the fuel still doesn't contact the valves to clean them is debatable (although I still use it).
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Old 02-08-2014, 10:47 AM
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Maybe because BMW calibrates F30 gasoline engines - N13, N20, and N55 - with RON 91-95 fuel, which generally corresponds to U.S. and Canada AKI of 89-91?
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Old 02-08-2014, 10:47 AM
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I would think that with DI, higher detergents would keep the injectors clean(er).
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Old 02-08-2014, 11:06 AM
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Quote:
Originally Posted by HELLR0T View Post
I put premium in all my car, required or not.


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Quote:
Originally Posted by cleaver View Post
I suspect it's to combat premature detonation or "ping." As with all turbo cars, the effective compression is much higher leading to higher chance of pre-ignition. The cooling effects of direct fuel injection helps to alleviate this (hence the high 10:1 compression ratio), but the higher octane of premium will help more. The lower octane rating is a minimum, beyond which I suspect the computer's timing parameters may not be able to compensate.
Premium fuels also usually have higher levels of detegents, but whether that will do any good when the fuel still doesn't contact the valves to clean them is debatable (although I still use it).
^ this. High compression motors require higher octane gas to avoid premature ignition and thus knocking.
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Old 02-08-2014, 11:59 AM
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Originally Posted by tturedraider View Post
^ this. High compression motors require higher octane gas to avoid premature ignition and thus knocking.
N20 compression ratio is no higher than the n52 which could run on regular. Both are not that high.

I suspect that BMW assumes that US premium gas is cleaner and has a problem with ethanol.

http://www.minotdailynews.com/page/c...id/575433.html

Last edited by Saintor; 02-08-2014 at 12:05 PM.
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Old 02-08-2014, 12:13 PM
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N20 compression ratio is no higher than the n52 which could run on regular. Both are not that high.

I suspect that BMW assumes that US premium gas is cleaner and has a problem with ethanol.

http://www.minotdailynews.com/page/c...id/575433.html
In the U.S. BMW calls for premium/91 octane in the N52 motor also. As they did for the M54 motor in the E46.
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Old 02-08-2014, 12:20 PM
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Originally Posted by tturedraider View Post
In the U.S. BMW calls for premium/91 octane in the N52 motor also. As they did for the M54 motor in the E46.
BMW recommends premium but 87 is the minimum required.

As for the N20 if I understand what I read above, 89 is required.
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Old 02-08-2014, 12:32 PM
HELLR0T HELLR0T is offline
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Great article in the topic

http://lifehacker.com/5846880/should...-gas-in-my-car


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Old 02-08-2014, 01:27 PM
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Originally Posted by gkr778 View Post
Maybe because BMW calibrates F30 gasoline engines - N13, N20, and N55 - with RON 91-95 fuel, which generally corresponds to U.S. and Canada AKI of 89-91?
I think I've figured out the answer, thanks to this and other fine bimmerfest posts. I don't have any laboratory proof, though.

My theory:
The N20 in the F30 can obviously be calibrated for different output. In the 328i, it's advertised as 240 hp but actually is (numbers made up) 240 hp/91 octane and 235 hp/89 octane. For the 320i, it's (again, numbers made up) 180 hp/91 octane and 176 hp/89 octane. For both cars, it's optimized for 89-94 octane. Putting 96 octane won't increase output. For this engine, they could have calibrated it to accept 87 octane but then it would only have benefited from 87-92 octane because the range of acceptable octane is limited.

Again, this is only a theory. Makes any sense?

For some drivers, it would have been better if the car were calibrated to accept 87 octane, especially in those areas with only 91 octane.

Contrary to many people's claim, using slightly higher octane gas can result in better gas mileage. I've noticed it. The EPA tested it and found the same to be true. However, the improvement in gas mileage was often only 1 mpg, not enough to offset the higher cost of premium gas.

Around here, there's 87, 89, and 92. 91 and 94 are available in Vancouver. I choose 92 because I don't want to pay a huge amount more for 94 and likely see little or no difference. Any experience with Chevron 94?

I've seen 85.5 in some Rocky Mountain states.

I once put some Aral 102 octane in the car while in Germany. I think 102 is about the same as 97 on the octane scale used in the U.S. and Canada.
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