[s-cars] Spark Plug Gap

[Kirby Smith]

Huh?! Spark is retarded with higher pressures because the propagation
speed of the flame front is faster and one doesn't want the front to
reach the piston too early.  The timing should be independent of the
size of the spark.

The spark size (width) is determined by the energy in the pulse, the
gap, and the pressure (and likely other stuff such as mixture).  Until
the energy is high enough to saturate the available free electrons in
the gap, the arc will not grow materially larger.

If the voltage available is high enough, i.e., from a capacitive
discharge ignition, the gap can be lengthened over what an old time
ignition coil/points setup can manage for the same pressure.
Conceivably one could replace the present drive electronics with a
higher energy system that would allow further gap.  However, with a
system designed by Audi for stock pressure, I certainly wouldn't
lengthen the gap for use a higher-than-stock pressure unless I knew
there was a lot of margin.

kirby

Bruce Mendel wrote:
>
> This is a multi-part message in MIME format.
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> I am running 25lbs of boost in RS2 setup. What gap is everyone typically using in high boost setup with Bosch plugs?
>
> I am at .032 gap, and not getting any missing, but wondering if I am leaving power on the table by having timing retarded if it's not giving me biggest spark possible to ignite the mixture.
>
> Thanks!
>
> Bruce
> 93 S4
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