87 Octane Vs. 91 Octane

[california]

Hi Folks,

I have a 2001 year 325i BMW . Does someone in this Forum tell whether it makes any difference in using either 87 Octane or 91 Octane Gas for my car(i always go for 91 octane).Gas prices in california are ghead .I usually drive in the city traffic conditions and sometimes though very rarely hit 90-95 Miles/hr on highway.

Thanks for the advise!!

[warell]

I have a 2000 328 and I do 91.. But I understand being in LA about those California gas prices.. But I have done 89 on occasion but I would never do 87..

[Furious]

never use anything other than what the manual tells you to use, there is a reason, the main one is a few years down the road when your maintance schedule gets a little busier.

[PMB]

I have a 99 328iSE and 91 is the recommended, 89 if you have to (runs a little rough) 87 is basically kangaroo juice.

I don't feel sorry for you with gas prices. It costs me just short of $100 to fill with 91 octane gas. I bet you don't feel so bad about LA prices now!

[storme]

WOW

here in the uk we are told in our manuals to use 98ron octane
and our lowest is 95.

[97alpineM3]

Ok... speaking from only what I know.. and I might be wrong... so someone correct me if I'm wrong here..

The different levels of octane in gasoline tell you how much fuel can be compressed before it spontaneously ignites. So... this is the down low so you can tell them the exact answer... Gas is comprised of crude oil.. then it goes to the refinery.. and then you get .. what they call hydrocarbon chains of different lengths... then its blended to form different types of fuels acourding to the length of the chain... such as butane... methan... and propane... and of course gasoline... well I know I'm getting on a tangent.. but octane is just one of those lengths of crude oil.. it can be compressed to a very high ratio before it combusts... so if your running 93 octane... thats 93% octane and 7% heptane... and will combust at a given compression ratio... so thats why you need to use a certain gas in a certain engine... all is relative with compression and octane. A higher octane fuel though... will be able to compress to a higher ratio.. therfor making your engine run at a slightly higher compression so it can combust after it mixes with H2O.



Thats some information I wrote about a year ago on this forum... should explain some stuff about octane that might pertain to your car...

Les

[BimmerDom]

Originally posted by storme@Jan 28 2005, 02:34 PM
WOW

here in the uk we are told in our manuals to use* 98ron octane
and our lowest is 95.

[snapback]281093[/snapback]

Your Octane ratings are not measured the same way as in North America, we use CLC, not RON.

eg:
87CLC octane ((RON+MON)/2) = 91 RON

[BimmerDom]

[california]

I came across this website that explains the issue.I may be wrong but its the opinion of the people.

http://lotus.roadfly.org/turboesprit.../msg01047.html

[Bear]

First is it 91 RON or 91 AKI you are talking about (we need to separate the apples from the oranges). In the US the octane rating at the pump is AKI (a blend of RON or the Research Octane Number and the Motor Method Octane Number that gives us the AKI or Anti Knock Index). In the real world, a 91 RON equals a 87 AKI and unless your car is certified for or has been modified for more timing or a faster timing advance, higher octane will only help the seller of the fuel.

[peterkulesza]

last post very true, but:

do not use octane lower than indicated by bmw as minimum (whetever particular country specific rating).

there is a limit to what knock sensors can do, with too low octane you can terminally overheat (warped or cracked head, cracked porcelain in the plugs etc).

so: no benefit from octanes above the necessary (in our stock or near stock cars), but potential bad problems if minimum not met.

peter

[Bear]

Very true about use what the book recommends, but be sure you understand the book, RON versus AKI. Another thing about premiuum fuel is it vaporizes or burns slower than regular grade fuel and can cause initial start up stalling in cold weather. My daily driver is a 1998 Neon with, among other mods a reflashed computer requiring a minimum of 91 Octane fuel and in very cold weather the first start of the day is a start and die, restart. In fact, Chrysler has a TSB on this subject (140897).

[peterkulesza]

fascinating.

i thought the evap problem is no longer true: this was notoriuosly true when they used aromatics to enhance octane numbers (those have extremely low evap).

dose the neon still suffer ? are you in virginia? the gas formulation for winter varies among states....

[EnvyM3]

I only use 93 in my car and 95 if it is available. The higher the octane, the better it performs and it is much better for the engine.

[9inarow]

I have to agree. Don't use anything less than what the instruction manual tells you to. These high performance engines need alittle more omphf.

The difference between 91 and 87 octane is about 20 cents per gallon. That's about $2 for 10 gallons or $4 for 20 gallons. Cut back a few cups of coffee and spend the money on your car.