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<p>Paul,</p>
<p>Thanks for that good explanation.</p>
<p>David<br>
</p>
On 5/2/2018 2:38 AM, PaulHunt73 via Mgs wrote:<br>
<blockquote type="cite"
cite="mid:2BAFF5F88B354081AD1F4A70167C3FF1@paul">
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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> </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> </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> </div>
<div><font size="2">PaulH.</font></div>
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<div style="FONT: 10pt arial">----- Original Message ----- </div>
<div><br>
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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>
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