Is this an M90?

[Bmachine]

From https://en.wikipedia.org/wiki/Octane_rating:

Anti-Knock Index (AKI) or (R+M)/2
In most countries, including Australia, New Zealand and all of those in Europe,[citation needed] the "headline" octane rating shown on the pump is the RON, but in Canada, the United States, Brazil, and some other countries, 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 Posted Octane Number (PON).

Difference between RON, MON, and AKI
Because of the 8 to 12 octane number difference between RON and MON noted above, the AKI shown in Canada and the United States is 4 to 6 octane numbers lower than elsewhere in the world for the same fuel. This difference between RON and MON is known as the fuel's Sensitivity,[4] and is not typically published for those countries that use the Anti-Knock Index labelling system.

"Regular Gasoline" in Australia, New Zealand and the US: 91–92 RON = 87AKI
"Premium" or "Super unleaded" gasoline in US (10% ethanol blend) 97 RON = 92-93AKI

 

[WISE9UY]

This is getting to be great information. I had wondered why the pumps show RON (R+M). That starts to make sense of things. Thanks for chiming in. I had looked at the wiki and online info before when I was wondering why the octane seemed so low here but had not made sense of it. What threw me is that the pumps still reference RON (R +M) rather than simply calling it AKI, which now is apparent to me that it is. Good to know that the gas is not so much worse here after all. So then I wonder why BMW didn't bring the S50/B32 motor here? That is a very high compression motor and I had started to convince myself it was because of octane availability. Maybe it is more to do with emissions then?

 

[rsporsche]

i would guess 2 reasons - one their market analysis and our low speed limits of the time ... and their fear of maintaining a car within the emissions laws

 

[Layne]

So then I wonder why BMW didn't bring the S50/B32 motor here?

I read it was partly due to cost cutting, as they would sell a very large number at relatively low prices in the US, plus we had the 55mph speed limit when they first came out.