CA's max is 91.

Maybe the rating system is different in the US, but our premium is either 98 or 95 RON depending on which brand servo you go to.

We haven't seen 93 octane here in CA for many years. That's the highest I remember seeing since I started buying gasoline 24 years ago. Not sure I'd want to may for that at this point anyway. Regular unleaded (87 octane) was up at $3.45/gal at my last fill-up. That was the second time it cost me more than $50 to fill up the 15.9 gal tank in my 4runner. Maybe it's time to sell the beast.

Maybe the rating system is different in the US, but our premium is either 98 or 95 RON depending on which brand servo you go to.

It is. We use AKI (Anti-Knock Index) which is an average of RON (Research Octane Number) and MON (Motor Octane Number.) That generally works out to 2 or 3 points less than RON. So at best, figure our 91-92 AKI as about the same as 94-95 RON.

You can retard the timing a few degrees. I would check your total timing first, not what it is at idle. I would try retarding 2* to start with. Pulling timing will hurt power a little but if you are on the edge of knock it shouldn't take much and the power loss shouldn't be noticable.

It is. We use AKI (Anti-Knock Index) which is an average of RON (Research Octane Number) and MON (Motor Octane Number.) That generally works out to 2 or 3 points less than RON. So at best, figure our 91-92 AKI as about the same as 94-95 RON.

I believe it is actually a 4/5 points difference.

Europe has 98 and 95 RON equaling 93 and 91 here in the states. My 1971 Datsun Haynes manual says that the 240z should run on 98 ron (93 here in the states) and the 260z should run on 94 Ron (being 89/90 here in the states.)

Here in TN, we have 87/89/93. I really don't see the need for 89. Usually if you need something higher than 87, you need at least 91. I have never seen an application where 89 was the minimum required to run the car. I have only seen it be 87/91/93.

At stations they should do the whole country a favor and replace 89 for E85.