Re: air - fuel ratio

jim wrote:
> 
> Dyno wrote:
> 
>> Jim,
>> Octane rating has very little to do with fuel economy. Performance,
yes.
> 
> Having AF ratio designed to maximize efficiency in the catalytic
converter
> doesn't have much to do with fuel economy. When fuel economy starts to
> really matter the catalytic converter is going to be replaced with
systems
> that burn the fuel inside the engine and deliver it to the wheels. And
> octane will matter.
> 
> -jim
> 
Seeing as how 99%+ of the fuel already IS burned in the engine, I don't 
agree with your assertion.

Octane rating is related to the susceptibility of the fuel to 
auto-ignition. This is generally most significant at high-load operating 
conditions.

When I think of fuel economy, I think of light-load operation; cruising 
down the highway or driving around town. On a time-weighted basis, under 
these conditions engine loads (BMEP levels) are relatively low. It is 
also at these conditions that the octane requirement is also low. 
Increasing the octane rating of the fuel will not alter the energy 
inherent in the fuel nor will it boost fuel economy.