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<DIV><FONT size=2>Ignition systems have for decades been more than capable of
generating a spark that will jump gaps much bigger than the plugs we use,
up to 1/4" in my tests with the system as used in the MGB and cars of that
era. However that generates very high voltages which can break down
ignition components like cap, rotor, lead insulation and even the coil.
It's the size of the plug gap plus that between rotor and cap contacts which
determines the peak voltage in the ignition system, and it's the
requirement for that peak voltage not to exceed a certain
amount that leads to the manufacturer specifications for plug
gap.</FONT></DIV>
<DIV><FONT size=2></FONT> </DIV>
<DIV><FONT size=2>When an ignition coil generates a spark it generates a certain
amount of energy which is dependant upon the design of the system, and
modern electronic ignition systems generate a lot more energy than
ours. If a lead is removed from a plug with the engine running
this will generate voltages much higher than ours - so much so that they come
with health warnings, but the plug gap has typically only increased by a few
thousandths of an inch. </FONT></DIV>
<DIV><FONT size=2></FONT> </DIV>
<DIV><FONT size=2>When an ignition system fires the voltages rises over time - a
very short time. When it reaches the breakdown voltage of all the air-gaps
in the system i.e. plug and cap to rotor (where applicable) the plug fires and
current starts to flow. At that point the voltage doesn't rise any
further, the energy starts to dissipate as current, and the higher the
energy produced by the system the longer the current will flow. It's
the duration of the spark that is more relevant to modern high-energy
systems than the length of the spark i.e. plug gap.</FONT></DIV>
<DIV><FONT size=2></FONT> </DIV>
<DIV><FONT size=2>PaulH.</FONT></DIV>
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style="BORDER-LEFT: #000000 2px solid; PADDING-LEFT: 5px; PADDING-RIGHT: 0px; MARGIN-LEFT: 5px; MARGIN-RIGHT: 0px">
<DIV style="FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV><FONT size=2></FONT><FONT size=2></FONT><BR></DIV>I always thought that
the larger gap gave a bigger spark and was better, as long as the system
generated a spark capable of jumping that far. The gap was a compromise,
big enough, but not so big that you end up with no spark. Modern cars
are more capable of reliably handling the larger gap.</BLOCKQUOTE></BODY></HTML>