Confused about petrol

[Sheytoon 0]

Hi All,

Now this may sound like a stupid question, but as i always say there is no such thing....

I’m a bit confused ( ) as to whether I should be using 91 or 98 fuel in my M3. I was reading a post here

http://www.theautochannel.com/news/2006/04/16/004226.html and it stated that it uses 91....Now I’ve been using 98. Is it better to use 91 for my BMW?

I always thought 98 would give you more power and be better for your engine?

[3 SERIES 93]

Definitely 98

[Ben 0]

I didnt read the article but the site looks to be american

they dont get as high octane fuel as us. I think 94 is the highest in usa.

To answer your question a fuel with a higher octane will help prevent detonation

better than a fuel with a lower octane rating.

I would use 95 as a minimum in your m3 with its high compression.

use 98 if price isnt a worry

[*Glenn* 854]

A minimum of 95...but I would use 98

[westy 614]

I didnt read the article but the site looks to be american

they dont get as high octane fuel as us. I think 94 is the highest in usa.

Close. They use a different rating to us. Ignore it.

OP use 95-8.

Edited January 27, 2011 by Westy

[Sheytoon 0]

Thanks all. I'll continue to use 98 then (even if the price is ridiculously high)

See you all this Monday

[Grant 4]

Close. They use a different rating to us. Ignore it.

OP use 95-8.

I was going to say that,

We get three octane ratings here (the US) 87, 89 and 91 but a different method of measurement. See below (from Wikipedia)

Research Octane Number (RON)

The most common type of octane rating worldwide is the Research Octane Number (RON). RON is determined by running the fuel in a test engine with a variable compression ratio under controlled conditions, and comparing the results with those for mixtures of iso-octane and n-heptane.

Motor Octane Number (MON)

There is another type of octane rating, called Motor Octane Number (MON), or the aviation lean octane rating, which is a better measure of how the fuel behaves when under load, as it is determined at 900 rpm engine speed, instead of the 600 rpm for RON.[2][3] MON testing uses a similar test engine to that used in RON testing, but with a preheated fuel mixture, higher engine speed, and variable ignition timing to further stress the fuel's knock resistance. Depending on the composition of the fuel, the MON of a modern gasoline will be about 8 to 10 points lower than the RON, however there is no direct link between RON and MON. Normally, fuel specifications require both a minimum RON and a minimum MON

Anti-Knock Index (AKI)

In most countries, including all of those of Australia and Europe the "headline" octane rating shown on the pump is the RON, but in Canada, the United States and some other countries, like Brazil, the headline number is the average of the RON and the MON, called the Anti-Knock Index (AKI, and often written on pumps as (R+M)/2). It may also sometimes be called the Road Octane Number (RdON) or Pump Octane Number (PON).

Difference between RON and AKI

Because of the 8 to 10 point difference noted above, the octane rating shown in the United States is 4 to 5 points lower than the rating shown elsewhere in the world for the same fuel.

[Grant 4]

^ on that note, as far as the price difference in concerned, there seems to be about US10c a gallon difference between the grades.

91 currently costs around US$3.30 - US$3.50 a gallon (about NZ$1.20 a litre)

89 - $3.20 - $3.30 a gallon

87 - $3.10 - $3.20 a gallon

This is in California. In other states it is significantly cheaper again. California has the highest cost by some margin in the USA (for most things).