On 22/08/2015 10:28, The Natural Philosopher wrote:

snip

The final point being the engine is designed and mapped for one
particular grade of fuel. And tested to ensure that others don't cause
problems, but it is not optimised for them. All cars will run best on a
particular grade and better or worse on others.

So "However a car adjusted to run on low grade fuel either by fixed
design or automatically will still run better on better fuel" is
complete nonsense. Better fuel inferred to be higher octane.