Different methods of calculation from what I understand. Amoco is all I've ever used in my performance cars (although it's sold under the BP name now). Can't do better than 93 in most areas, and CA folks are just SOL :)

Looking at it from another perspective, I suppose some might say if your car can't run on 87 you're sol too.

Nah, we just put those "wimpy" stock chips back in when we visit CA :)

The 3.2 cars don't have knock sensors so the rule is pretty clear. You run enough octane that the engine doesn't detonate at all. Any more then the minimum and you are just spending extra money unless the higher grade has a better additive package. (Chevron used to put more Techron in the Premium grade. Not sure if that is still true.)

You can't hear subtle detonation (especially in an aircooled motor) but it still causes problems. If you can tell the difference then you should go up a grade.

Around here we have Chevron 87, 89, 92/93. My book says use RON 96, and 92 rating for pumps in the USA, '86 3.2. I think maybe anyone burning anything under 91 should rethink things? :)

The Amoco (BP) 93 around here used to be the "white gas" many years ago. It's still clean stuff...when I went to a local foreign outfit to pick up some some Techron, the owner asked me which gas I used, and I told him Amoco 93...he replied "don't waste your money on the Techron...don't need it". I still run a bottle through on occasioin. What the 93 octane allows us to do is to run a chip that's programmed to take advantage of the additional octane, boost performance a bit, and still protect the motor. Heck, my prior sports cars had factory chips that required 93 (or was it 91) as I recall, I don't pinch pennies with expensive motors :).

Unless you have a performance chip or anything other than a stock engine, run 87. There is absolutely NO performance gain from a higher octane. High octanes are used to prevent knocking. Turbocharged cars and N/A cars with their ignition timing advanced are some examples.

Before I installed a SW chip, I ran 87 for many years with no ill effects or performance decreases.

I'd suggest that people take a look at their owner's manuals, or the octane sticker on the car, before assuming that 87 is good for everyone. There were some changes made to the Carreras during the 6 years they were produced, so they are not all the same. Also, cars with higher mileage can have carbon buildup in the cylinders, they can burn oil from the valve guides, they can have other defects that make them less tolerant to lower octane. Most people can't hear detonation in a 911 motor, unless it is severe. How experienced are your ears?

As others noted, some gasoline brands include better additive packages in their higher grades of gas, so that's another thing to consider.

Caveat emptor.

JR