Re: air - fuel ratio

Dyno wrote:

> 
> I was all set to fire off a followup, but you beat me to it, almost
> point by point. A lot of the nonsense that gets posted could easily be
> avoided is some posters would simple go buy an engine text book and
> simply browse through it.

Here is what you said on how octane affects fuel economy.

> 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.

	 If you read your engine textbook you will find that the RON rating is
made under light load conditions just as you describe. You are correct to
say driving consistently under light load is how the best fuel efficiency
is achieved and because of higher fuel prices more people are driving like
that. Driving at 45 mph instead of 70 mph significantly reduces engine
load and may as much as double some vehicles mileage if given the right
fuel.  The fuels properties to knock under light loads is exactly what the
RON test determines. Engines do knock under light loads even if you think
they don't ( and even if you can't hear it) and that does impact on gas
mileage.   

	The problem is you don't have any idea what the RON rating is for the
fuel in your gas tank and it can vary quite a lot for any given posted
pump octane rating. But in spite of the fact that you have no idea what
the octane is in your gas tank under those conditions that could
potentially be giving you better mileage, you are positive it has no
affect on mileage cause you read something in a book.

-jim


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