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 these results with those for mixtures of isooctane and n-heptane.
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. MON testing uses a similar test engine to that used in RON testing, but with a preheated fuel mixture, a 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. Normally fuel specifications require both a minimum RON and a minimum MON.
In most countries (including all of Europe and Australia) the "headline" octane that would be shown on the pump is the RON, but in the United States, Canada and some other countries the headline number is the average of the RON and the MON, sometimes called the Anti-Knock Index (AKI), Road Octane Number (RdON), Pump Octane Number (PON), or (R+M)/2. Because of the 8 to 10 point difference noted above, this means that the octane in the United States will be about 4 to 5 points lower than the same fuel elsewhere: 87 octane fuel, the "regular" gasoline in the US and Canada, would be 91-92 in Europe. However most European pumps deliver 95 (RON) as "regular", equivalent to 90-91 US (R+M)/2, and even deliver 98 (RON) or 100 (RON).
Most stock cars can -- and should -- use "regular" gas, but most modded cars need the highest available octane.bonakdar said:93 RON would be about 89ish octane (US), 95 RON around 90-91 ish octane (US). If you want a 98 RON equivalent, you can use Sunoco's 93 Octane (US) gasoline. But 91 Octane (US) is sufficient..... I run the 93 octane in my car not for any reason other than the gas station is on my way to work and its about the same price as mid-grade at Shell or Hess in my area (boston).
I think Ultra varies depending on region. I used to work at a Sunoco in Reading, PA and we sold a lot of Ultra on the full-serve side, mostly due to my winning charm Ours was 94.JugGerNaut said:i just filled up at sunoco and i could have swore it was 94 octane, expensive as hell though...