At 01:34 PM 5/22/98 -0700, you wrote:
>What causes Knocking/Pinging under hard acceleration? Bad Mixture? Low
>Octane? Not enough Spark? Bad Timing? < snip >
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Kirk,
It's not quite that simple. Every thing you mentioned, with the exception
of not enough spark, can cause knocking. Knock, in simple terms, is an
uncontrolled explosion instead of a controlled one(smooth flowing from the
top of the cylinder down). Too high a compression for the octane of fuel
your using will cause it. This is one of the many misconceptions about
using ONLY high octane fuel thinking it's better. It actually burns SLOWER
to prevent detonation in higher compression situations, so if you don't
need the octane to prevent detonation, your wasting your money. Timing
that is too far advanced (again for your engine conditions) will cause
detonation. A too lean condition can also cause detonation. If you have
the factory engine settings correct for the car (timing, mixture cam etc.),
and haven't changed the compression ratio any then I would suggest a higher
octane fuel. You could always back off the timing a little from what you
currently have it set at, but you must be careful here. More than say
about six deg from optimum, and you run the chance of starting to over heat
or run hotter. Basically when you run the timing too far in retard of the
optimum setting you are losing power by burning fuel in the exhaust system
as waste heat instead of the cylinder where it should be pushing the piston
down-
Barry Schwartz (San Diego) bschwart@pacbell.net
72 V6 Spitfire (daily driver)
70 GT6+ (when I don't drive the Spit)
70 Spitfire
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