Octane Ratings in South America

Octane requirement is based on many things, but the main factors are; cam duration, compression ratio, elevation, head design, and ignition timing.

as cam duration increases, octane requirement tends to decrease, but since most factory engines have very mild cams it doesn't really factor into this discussion. As compression ratio increases, octane requirement increases. Higher elevation reduces the need for octane. Head design (in particular combustion chamber design and what metal is used) affects octane. For a given combination, an aluminum head typically needs less octane than the iron since aluminum accepts heat at a much faster rate. Ignition timing is also pretty much at the limit for most modern engines so they are optimized for the rest of the engine. Higher performance typically means engine parameters that require higher octane, but the manufacturer rarely designs an economy engine that requires premium fuel since its owners aren't willing to pay the big money for the fuel.

What isn't discussed in actual "real-world" requirements is all the other stuff. Its quite possible that a Toyota Camry destined for the US recommends 87 octane while the same exact Camry shipped to England requires 93 octane. Why? Several reasons might come into play. First, octane ratings differ depending on how they're measured. In the US we measure octane by the R+M/2 method where research octane and motor octane are averaged. Other areas use just the R number. The same exact fuel that tests 87 octane in the US might test 91 octane somewhere else. Another very prevalent factor is the law. US warranty law has different criteria to determine whether or not warranty claims have to be honored based on fuel-related damage compared to other countries. Its possible that our subject Camry requires premium fuel so that Toyota can legally cover their butts. In truth it doesn't require any more octane, but financially it was determined that requiring higher octane was a legally sound move in some locations.

Excellent answer! Thank you very much.