Chris,
     If your van is knocking on regular and you add a
higher octane and it stops knocking what does this
tell you about your combustion chamber?   If your van
is not knocking on regular, burn regular and save your
money for better things like something to clean your
fuel injectors because higher octane is something that
takes most of us to the cleaners.   happy new
years,gary
Date:    Thu, 27 Dec 2001 16:35:28 -0600
From:    Chris Stann <ChrisS@INFORMS.COM>
Subject: Re: Subject: Fuel octane

Some info contained here:

http://www.pcf.ab.ca/quick_answers/gasoline_general/octane_rating.asp

And here:

http://www.shellus.com/products/product_info/gasoline_properties.html

"Probably the most familiar gasoline characteristic is
antiknock
quality or
its octane rating. The octane rating is simply a
measure of the
gasoline�s
resistance to knock. Knock is the sound made when the
fuel/air mixture
in
the engine�s combustion chambers ignites by itself
(auto-ignition),
either
before the spark occurs or in front of the flame
already started by the
spark plug. Advancing ignition timing increases the
tendency to knock.
"

It says absolutely nothing about the higher-octane gas
burning at a
higher
temperature.  It does say, however, that engines with
higher
compression,
such as Euro-WBX, or advanced timing, such as mine,
will benefit from a
higher octane gasoline.  Also, engines with combustion
chamber
deposits,
such as any old WBX, will have slightly higher
compression ratio, hence
the
benefit of increased engine longevity from
higher-octane gasoline.

All of this should be considered along with the
driving environment.
It
seems that an engine under higher and prolonged loads,
such as a
hill-climbing Westy, is probably going to benefit from
the more
expensive
gasoline.

Chris.

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