Octane Confusion

Hello,

What is the difference between the R+M/2 and RON? Manufacturers always seems to give two different octane ratings when recommending fuel types. So which one are you supposed to follow? RON always seems higher than R+M/2. What does RON mean? Research Octane Number?? And what is that supposed to mean as opposed to R+M/2?

Post edited by: onanysunday, at: 2007/09/24 13:52

RON is the theoretical octane value, based on the ingredients that went into the gasoline. RON is the R in (R+M)/2.

MON (Measured Octane Number) is the actual measured octane value of the gasoline.

The average of MON and RON is what you see posted on the gas pump.

As payment for my help, you are now required to go listen to the CD "Octane" by the band Spock's Beard.

Nice explanation, tj.
Although I'm starting to believe that all three pumps are being fed by the same big tank in the ground. It'd be a hoot to show up at the pump with one's own personal octane tester. Wonder how close to the advertised octane it really is?

So, for example..A manufacturer writes something like "recommended fuel is 87 (AKI), 91 RON"

Which one to believe? Which one to use?

Also, Why don't they measure the fuel according to the 'actual' MON only, and not by the 'theoretical' RON? This doesn't make sense. Who cares what octane rating its supposed to have in a laboratory? It seems to me all that matters is what is directly measurable when the gas is actually pumped into your tank. Gentlemen, My question is twofold:

1.)Who makes these rules?
2.)Are they on crack?

Post edited by: onanysunday, at: 2007/09/24 18:07

onanysunday wrote:

So, for example..A manufacturer writes something like "recommended fuel is 87 (AKI), (91 RON)"

Which one to believe?

i believe they are the same thing. 87 AKI equals 91 RON:

en.wikipedia.org/wiki/Octane_rating

So when you fill up would you go with the 87 or the 91?

onanysunday wrote:

So when you fill up would you go with the 87 or the 91?

i'm in canada which uses the AKI octane measure.

87 is regular gas, 91 is premium gas, and 89 is a blend of the two.

my kz1000 owners manual says to use '87 octane or higher'. an old school mechanic suggested i use 89, so that's what i use.

(in canada sunoco also sells a 94 octane gas that's 10% ethanol.)

Post edited by: duncan, at: 2007/09/24 17:40

Ok, so you just average out the two numbers according to manufacturer specs? :huh:

I'm reasonably certain that the (R+M)/2 method is required in the US by Federal regulation.

At the Ford ASSET program, they basically said in a stock engine, to run the lowest octane you can without getting spark knock. The higher Octane number refers to the fuel's increased RESISTANCE to combustion due to added detergents. Since detergents don't burn, the less you can get by with, the better power and economy you get. I personally run 87 (R+M/2 as stated on the pump) which is sold as regular, and have yet to have ANY mechanical problems EVER related to fuel quality.

del