In Japan, here in NZ, in AU, and as far as I know, the rest of the Asia pasific region, the fuel is measured by the RON number.
We have 91, and either 95 or 98 available here.
The Japanese used to have 96 or 100, but I believe this has changed?
The higher octane available in Japan meant Japanese domesitc market cars could run higher compression ratios and more advanced timing that models built for export.

Now if your an excutive in charge of building cars in America, and you know that some of those cars are going to the US market, some are going to the Japanese market and some are going to the UK, do you fit each with a different engine?
Is it worth the extra cost of developing a different level of tune for the Japanese market car and having to do 2 or 3 different production runs at the engine plant?
I would think it would be easier to just use the exact same engine in all 3 models.



I might get hold of a compression tester and see what the numbers are.

 

Higher octane fuels are less likely to knock. So you can add more ignition timing and gain some power. Keeping ignition set at stock = nothing. Wont hurt any thing to run 91. Some cars require high octane such as high compression engines and turbo stock set ups.

 

Different engines are common for different markets, even on the same assembly line. Besides, there's all kinds of other equipment that's different, like lights, RHD, & mirrors.