At 02:20 AM 2/15/2003, Ben McCafferty wrote:
>No, I think you're right and we're saying the same thing.  Now I'm really
>reaching here back to high school physics, but if I recall correctly, it
>takes about 20,000 volts to jump 1 centimeter.  Can someone confirm or
>refute that?

Should be about right -- in dry air, at one atmosphere, using ball
electrodes of some diameter I forget.  Need less voltage as the electrodes
get pointier, more as the air is compressed.

>  In any case, if it takes more volts to jump a longer distance,
>a larger gap would mean higher voltage before the spark would get across,
>and a smaller gap would mean lower voltage to get across.

Yes.  Which will affect the timing by the difference in how long takes the
voltage to rise high enough to fire the plug -- but that rise is fast
enough that I doubt you would be able to measure the difference easily.

>   I think that
>means smaller gap=quicker spark=lower voltage=cooler fire and larger
>gap=slower spark=higher voltage=hotter fire.

There is a correct gap to efficiently match the rest of the ignition system
and transfer as much energy as possible into the spark.  Beyond that I'm
sure there are other considerations that I don't know about...

david

--
David Beierl -- dbeierl@attglobal.net