Octane rating

I have a 1999 4.6. The owners manual says that using petrol with an octane rating of more than 95 RON will not increase performance or economy. This was written 14 years ago, and I ask if this is still the case for the modern high octane fuels. Has anyone seen any improvement when using 97 RON or higher?

Octane rating has nothing to do with the power output. It is the measure of how resistant the fuel is to compression ignition. Prevents pre-ignition on high compression engines. LPG for instance has an octane rating around 135 and cannot be ignited by compression only by spark.

Brimmed mine with Shell Optimax/V Power once.......performance did increase in the low and mid range but economy fell right off. Think I got around 240 to a tank and an average of something like 11.5 mpg (extra urban) where usually I can stretch it to 325/13.9 mpg.

It's like giving champagne to a hardened boozer.....they just don't appreciate it!

wammers said:

Octane rating has nothing to do with the power output. It is the measure of how resistant the fuel is to compression ignition. Prevents pre-ignition on high compression engines. LPG for instance has an octane rating around 135 and cannot be ignited by compression only by spark.

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Why's it called an octane rating if it's not to do with octane itself? Is it semi-archaic?