In article ,
Mike Barnes wrote:
I often fill up with 97 RON fuel (not 99, I've never seen that) and
although I don't monitor fuel consumption carefully, it's my impression
that it does give more miles per gallon than the usual 95. I'm also
pretty sure that the effect isn't great enough to make up for the
increased cost (often a bigger difference than the 4p you quote).

My engine was designed for 97 RON although it will run happily on 95.
The manufacturer's (Audi's) consumption figures refer to 97, which leads
me to believe that it's better than the figure for 95, but it might be
that they have to select same the fuel for performance and economy
figures, and choose best performance.

I travel to the North of Scotland quite often and usually do one way on 95
octane, and the other using Super 97-99 or whatever. I use the cruise
control where possible set at the same speed. And I can't honestly say
I've found a verifiable difference in either performance or economy. My
car is sort of the same as yours saying 95 octane on the filler but
suggesting in the handbook higher octane may be better. So I'd guess
*most* EU cars are optimised for 95 octane.

My old Rover, however, with no ECU control over ignition, objects loudly
to 95 but runs well on 97. Of course it originally ran on 4 Star leaded.

--
*Why don't sheep shrink when it rains?

Dave Plowman London SW
To e-mail, change noise into sound.