Spark Gaps In Series?

[russwr]

With a secondary spark gap (in vacuum chamber insulation), in series with spark plug, and using induction type ignition (not CDI), does the spark plug actually fire at the higher voltage of the wider first gap , so as it is at THAT minimum voltage for firing spark plug? It has to jump first gap before the 2nd. spark plug. Is there voltage drop loss affecting spark plug?

[Gary Hammond]

Hi Russ,

Not sure I understand your question. Using an auxiliary gap will require the voltage to reach a certain amplitude before the spark can jump across the spark plug gap which is under high pressure. This helps the engine to fire when the spark plug is carbon fouled from too rich of a fuel mix or when moisture is present. Most older, opposed twin cylinder, air cooled engines with battery ignition were arranged with the gaps in series. The spark would occur in both cylinders at the same time with one on compression and the other on valve overlap at just before TDC. I always set the spark gap in these engines at .025" because the two added together would be .050". I always set the gap in single cylinder engines at .030"

The newer twins have separate coils for each cylinder, so they can be set at .030" gap. The coil voltage will reach whatever value is required to jump both gaps at the same time (the gap resistances added together). However, the voltage across each individual gap will probably not be the same value.

Gary Hammond,

[mpgmike]

Automotive distributors have a gap between the rotor and terminal in the distributor cap. By default there's 2 gaps.