On Mon, 24 Jul 2000 13:11:26 -0500, Barney Gaylord wrote:
> At 09:36 AM 7/24/2000 -0400, Geoffrey Gallaway wrote:
>
> >I just bought a stock ignition coil from propermg for 19.95 although I
> could have bought the Lucas sports coil at 40,000 volts for a few dollars
> more. ....
> >
> >So, what voltage is the standard coil, 20,000 volts? How much does the
> sports coil actually gain? ....
>
> 17,000 to 20,000 comes to mind as standard, although I think a stock
engine
> may actually run (marginally) with as little as 7,000 volts.
>
> The voltage required to make a spark jump the gap at the plug is
determined
> by the size of the gap and by the pressure of the air in the cylinder.
> Bigger gap = higher voltage required. Higher compression = higher
voltage
> required. Once the voltage in the coil builds up to the required level
the
> spark jumps the gap and the voltage goes away. The voltage will never go
> any higher than what is required to make the spark jump the gap,
regardless
> of what coil you have. On the flip side, if the gap is too large, and
you
> don't have enough voltage available, then you will never get a spark.
The
> highest voltage requirement occurs at the point of highest dynamic
pressure
> in the cylinder, which for most engines is around 2500 rpm and full
> throttle, which is the same condition where you might experience spark
> knock with high compression and cheap gas.
>
> HOWEVER, when you have a coil that is capable of putting up a higher
> voltage, then you can open up the gap at the spark plug, which in turn
> demands a higher voltage to affect the spark, which in turn will give you
a
> higher voltage (and probably longer duration) spark. A hotter coil may
in
> fact be necessary in a high compression race engine just to make the
spark
> jump a standard size gap. With normal compression ratio and a 40KV coil
> you can open the spark gap from .025" to .035" or more and still get a
> reliable spark. The hotter spark will then make it easier starting and
> have much less probability of misfire under various running conditions.
> You would also be less likely to ever have fouled spark plugs. Also the
> system would be more tollerant of maintaince neglect, as it could fire a
> spark across a badly worn plug with a much larger gap.
>
> I happen to like my 40KV coil and .035" spark plug gap setting, finding
> easier starting, more consistent smooth idle, and never a misfire with
the
> hammer down. I think it's a keeper.
>
> Barney Gaylord
> 1958 MGA with an attitude
> http://www.ntsource.com/~barneymg
>
My understanding of a hotter coil is that it is capable of a little more
amperage accross the the gap to produce a hotter spark.
R. Sexson
74.5 B
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