ceboyd

Can someone tell me if this is correct:

These are different octane blends, rated with the same method, the US method.

EU ratings are 95/98, which are equivalent to US ratings of 91/93.

So, EU 95 octane = US 91 octane and EU 98 octane = US 93 octane.


Top performance with EU 98 octane = 93 US octane.
Small loss in performance with EU 95 octane = 91 US octane.


So on a 993, it needs minimum 91 US octane.

przt

RON Reaserch Octane Number. (Used in Europe and elswhere in gas stations)
MON Motor Octane Number.
AKI Anti-Knock Index. This is the number that is posted on the gas station in the USA as "Octane". It is derived as (RON + MON)/2

brucec59

Seems the highest octane I can find anywhere in NorCal is 91 (with the exception of the 100 octane stuff). Is 93 available commercially? What about octane booster additives? Or should I just forgetaboutit and keep driving?

Thanks.

STLPCA

Chris - you are correct. Using 91 AKI gas should result in a slightly retarded ignition w/a resulting loss of power on a stock NA 993.

As you know, the "octane number" is a measure of a fuel's anti-knock (or pre-ignition) characteristics.

There are different accepted standards used to measure the anti-knocking characteristics of gas. The octane number you see at US pumps is the average of two such octane numbers; the Research Octane Number (RON) and the Motor Octane Number (MON). This average number is sometimes referred to as the Anti Knock Index ("AKI") or the US Cost of Living Council method ("CLC"). The RON and MON numbers are determined by American Society for Testing and Materials ("ASTM") laboratory tests. Thus, US octane numbers are described as, e.g., 93 AKI or 93 CLC. The equivalent RON number in other countries would be 98.

The RON method determines low speed and low load knock characteristics while the MON method tests high speed, high load, high temperature conditions such as exist during periods of high speed power accelerations, hill climbing, or any period of high power output. The MON method results in a higher octane number & is the more relevant value for racing.

Maybe more than you asked, but ... .

ceboyd

o.k. thank you very muchfor explaining.

I know out west it seems more diffucult to get 93 octane at the local station but here in the midwest almost every gas station carryies 93 octane (only the cheapie gas stations carry 92 instead of 93) and some even carry 94 octane (like Sunoco for example)

nonzerosum

In Alberta, Canada - even though we are the oil capital of Canada, all of our fuel >91 octane has ethanol, which I have read may be a problem for our cars.

I've also read that you can consider the fuel's octane rating to be 1 higher for every thousand feet of altitude above sea level. I am only a lowly doctor. Any engineers out there to enlighten me?

ceboyd

so wait? The 10% ethanol in our 93 octane (been there for years) is bad for our cars????????

nonzerosum

Something about ethanol being hygroscopic and drying out seals. Like I said, any engineers out there to help shed light on this?

nonzerosum

hmm, just did a search. Try Steve W. of Rennsport Systems' posts about potential problems with ethanol and rubber seals. It may not really be an issue until our cars really age. But I'm still not clear if the 91 octane sold here (about 2.5k feet above sea level) can be considered about 92.5 octane on the coast.