octanes

[aotiko]

BMWs are supposed to run at 89 octane. But I heard from a rep at BMW that they only tell you that to make you feel like your buying an extremely high performance car when your car can run on 87 with no problems. I just wanted to know, i'm still going to put 89 in. Also, if I put anything higher than 89, will it make a difference or will it only make use of the 89 octane? That was pretty confusing wording, I hope someone can understand haha

[Bear]

I do not know what you are driving, but read the owners manual for AKI rating (the number you see on the pump). With knock sensors installed in todays cars, unless your car is cerified to run on 89 AKI or 91 AKI, the only gains by going to a higher AKI number is to the sellers pocket.

[TMac325is]

i used to always use 89, but then one day i decided to try out 91 and i could actually tell a difference in performance. it ran a lot smoother and seemed to accelerate better

[Live_the_Curves]

My performance and acceleration has never changed i ran with 91 octane for the first 5 months i had the car, then swtich to 87 NO DIFFERENCE. I heard if you have turbo in your car it make very big difference.

[Mr White G]

In the UK we have the option of 95 ron or 97 ron petrol.... this equates to 87 and 89 oct

Both work fine and premium (97 / 89) is preferred.

[EcianIce]

not sure where you get 89 as being premium. where i live we've got 93 oct.

i used 89 for a while, and got used to how it felt. mainly because gas was like 2.25 a gallon for a while.

after the prices got below 2 bucks / gal again. i started using 93 and felt the differance.

i alway suse 93. but im very positive the car will run fine with 89.

[aotiko]

i have a 325i, and I have been hearing that some people feel a difference and some don't. I think it's one of those things that if you take thier car and tell them you filled it with premium and filled it with regular, they will tell you there is a difference. It's all in their head.

[Relevart]

May be I am smoking a good stuff, I am not a chemist...
What about prolong exposure of BMW engine, fuel and exaust systems to low octain gasoline?
Can anybody knowledgable comment on accumulations of combustion by products on various sensors, pulluting engine oil, especially with long intervals between oil changes?
Technically, if compression ratio is less then 10:1 one can use 87 gasoline (US) with no problem. If compression ratio above 10:1, you will start hearing peinning noises from engine... and loss of power.

[peterkulesza]

sweet jesus please do not feed these nice cars low octane:

1. no, neither the current 2.5 nor the 3 liter is not supposed to use less than 91 octane (us). the compression ratio is these days a VERY poor guide for octane requirement. the engines are mapped to advance the ignition with 91 octane minimum in mind. is you put 89 or 87, you are running the risk of fatally overheating the head, and valves in it. this is because the knock sensors will be unable to compensate for the low octane, i.e. the computer can retard ingition only so far.

2. high octane prevents detonation in forward ignition advance (as all engines do to accelerate). normal flame propagation is about 30-60 cm/s. when you hear knock, you hear detonation i.e. flame advance of about 2000 cm/s. this first overheats the head, then ruins the main bearings through busting on the crankshaft.

3. octane rating has no relation to how clean is burns. if you are worried about deposits, use techron or some such thing. most brands in the u.s. have a ton of detergents, such that this is not a problem.

4. combustion products from any octane will acidify oil. hence, it is good to change oil every 5 or 10k, depending on city vs hwy driving. gas engines do not leave any particulates, so really there is no problem with this. all this assumes an engine with no blow by and in proper state of tune.

hope this helps

[doughboyea]

Originally posted by Mr White G@Jul 19 2004, 09:18 AM
In the UK we have the option of 95 ron or 97 ron petrol.... this equates to 87 and 89 oct

Both work fine and premium (97 / 89) is preferred.

This attached photo was taken in May of 2003, in Budapest, Hungary. I was looking at it and was wondering whether the fuel ratings were in Octanes... or is that only used in the US. I ask because I have a report to make on this to my professor at college.
Dough

[Bear]

As stated in my previous post, it is the AKI number, not the RON number you are concerned with. I have a 1988 750il and I use the BMW listed fuel(87 AKI). Maybe I should be worried about engine life, but at 130,000 miles she still runs just fine and remember, all US fuels contain a set amount of cleaning agents (as required by law) so we are running cleaner fuel today than we did 40 years ago. Do what you want, it is your money but higher octane numbers do not neciessarilly mean more performance and also the higher the octane, the slower the burn rate (she does not vaporize as quicklly as lower number ocranes) and she does emit more pollutants.

[Hoppy's535i]

octane is a mesuare of stability. the higher the octane the more stable the fuel is (under compression) as im sure you know. 91 octane acts more like 91% octane and 9%heptane

the benifits are in higher compression ratio engines.( includeing,as stated before turbos and supercharged engines)

so as was said before i dont think theres any differance in a stock engine.

[Mr White G]

This might go someway to clear a couple of things up. (Obviously some of you don't need it though, great posts! )

http://www.btinternet.com/~madmole/R...RONMONPON.html

[peterkulesza]

Originally posted by Bear@Jul 21 2004, 10:17 PM
Do what you want, it is your money but higher octane numbers do not neciessarilly mean more performance and also the higher the octane, the slower the burn rate (she does not vaporize as quicklly as lower number ocranes) and she does emit more pollutants.

all true few years back. the low evap was due to aromatics (benzene-based) blends which tend to have high octane numbers. us 93 octane is now blended from mostly aliphatics, so that it vaporizes as fast as lower octane blends.

also, the octane to heptane ratio (although still useful) is not how octane rating is currently tested. there are 105 octane fuels on the market (and you cannot have 105% octane liquid...). so there is a test device, where a particular blend or run to detonation, and the octane ratio inferred from the standards.

again, i must caution against using anything less than the bmw specified octane. penny wise, pound foolish imho.

p.s. no i don't work for big oil