In article ,
The Natural Philosopher wrote:
You don't 'adjust' an engine to make the best use of a high octane fuel.
You do if you are tuning for performance

It needs/allows things like a higher compression ratio.

And a more advanced spark.

That comes under adjusting. Since it can be done in software. Changing the
CR not.

You design the engine for a target octane rating. Knock sensors then
alter the mapping if a lower octane rating fuel is used. There is no
point using a higher octane rating than the engine is designed for.

You contradict yourself.

You design it for a target octane rating. Yes. You lower the mapping for
lower octane. Yes. so its NOW designed for the lower octane fuel!

Not so. It may run, but retarding the ignition for a poorer quality fuel
than it was designed for is at best a cludge.

I(f it has auto mapping it will definitely be better on the higher
octane. If not, its pretty LIKELY but not certain that it will be


What does of course happen is that if its running rich because the fuel
has more carbon in it - typically with aromatics, it will be leaned out
by the ECU so it will do better mpg on higher carbon content fuel.

The AFR on a modern engine is largely determined by the presence of a
catalytic convertor - not for maximum power or best economy.

As I said, its not that simple.

You've certainly proved that.

--
*Bigamy is having one wife too many - monogamy is the same

Dave Plowman London SW
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