[Mgs] spark plug gap

[David F. Darby]

Paul,

Thanks for that good explanation.

David

On 5/2/2018 2:38 AM, PaulHunt73 via Mgs wrote:
> 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.
> 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.
> 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.
> PaulH.
>
>     ----- Original Message -----
>
>     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.
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://autox.team.net/pipermail/mgs/attachments/20180502/c090dd37/attachment.html>