[mattkaenel]

Is there really a difference in performance difference between 87 octane and 91? I have been told it is all BS.

Is there any dyno results out there?

Thaks for the help.

[johnfkitchen]

Depends on the engine. In high compression ratio engines, a higher octane is required to avoid damage to the engine.

You should use what the manufacturer recommends.

[agarbati]

Do a google on AKF for different octanes. In general higher octanes are slower burning with higher AKFs (anti knock factor). Don't remember all of it but different octanes also have a different mode of propagation for the combustion front.

[e90fanatic]

just go for the highest octane you can get. My friends and I did a test. Differences between: 87 and 89 difference is quiet. 91 and 89 is power. 93 and 91 is power and quiet. So there IS a difference.

[ward]

If you're buying a BMW, don't be cheap.

you'll only save 2-3 bucks a tank, and your engine could be damaged if your knock sensor goes out. Your engine will not run at its rated power as it will de-tune itself to prevent knock with the cheap gas.

it is worth risking engine damage for savings of up to 150 a year????

[Robin_NL]

6 cilinder BMW's love high octane. I always get me RON98 here in EU. 95 will be fine/cheaper, but less power and less mpg.

[scottz5]

always used super in my e46, once the guy gave my wife 1/2 tank of reg and the car ran like crap.

[johnfkitchen]

Originally Posted by scottz5

always used super in my e46, once the guy gave my wife 1/2 tank of reg and the car ran like crap.

Had the same experience with six-cylinder E36. Since then, a diet of 93 when available, and NOTHING below 91.

[agarbati]

Excellent article for the un-initiated.

http://auto.howstuffworks.com/question90.htm

Some excerpts from searches for the lazy -

Octane is a measure of how well a fuel resists premature combustion, or “knocking.” Gasoline with too low an octane rating converts fuel to heat rather than power, making for less efficient fuel usage and reduced engine life.

The octane rating of gasoline tells you how much the fuel can be compressed before it spontaneously ignites. When gas ignites by compression rather than because of the spark from the spark plug, it causes knocking in the engine. Knocking can damage an engine, so it is not something you want to have happening. Lower-octane gas (like "regular" 87-octane gasoline) can handle the least amount of compression before igniting

[CC 330i]

My old car specified "UNLEADED FUEL ONLY" so I mostly bought 87.

My BMW specifies "PREMIUM UNLEADED ONLY 91 OCTANE" or higher so that is what I buy for it. The engine is designed for premium and has a higher compression ratio than my last car.

Always follow manufacturers recommendations. Will your car blow up if you don't use Premium? Probably not. But it may cause damage over time.

[crazybones]

There's a comparison at Car and Driver. The article is old (Nov 2001) but still valid.

http://www.caranddriver.com/article....&page_number=1

[weytie]

Now i understand why petrol is so cheap in US, it's only 87 or 91 octane.

Here in Belgium you have only 95 and 98 octane

Stijn

[timzerofive]

My old car was barely surviving on 91 octane. The guy at the shop actually told me when I first got the turbo done, that if I was to put anything less than 91 in, I would be back in the shop with busted motor in no time. CA gas sucks, especially for turbo cars. Is there really a noticeable difference between 87 and 91? Yes. Do I want to save 4 bucks on gas? Yes. Should I do that on a $45K car? No.

[Armen52]

Originally Posted by weytie

Now i understand why petrol is so cheap in US, it's only 87 or 91 octane.

Here in Belgium you have only 95 and 98 octane

Stijn

Actually weytie, if we were talking in the other GIANT thread regarding octane (search before you post people), I recall somebody posting to clarify this matter.

It seems that the octane rating method is not the same for US and European fuels. The US rating is an average of both RON and MON IIRC and the Euro is just the RON.

[E90Fleet]

The USA shows [RON+MON]/2 and europe shows RON

So 91 in the USA is about the same as 95 in europe