Plugs 101...after school

[rocco16 at sbcglobal.net (Larry Fry)]

I think the error in Allyn's theory is in assuming that the electrodes in
"copper plugs" are copper (is that right, Allyn?).  If so....
They aren't.
They are a nickel alloy.
The copper is inside the plug.
Why?  Because, as Allyn said, the copper would be erroded very quickly by
the spark AND the heat from combustion would melt a copper electrode.
Nickel has a much, much higher melting point, that's the main reason it's
used.  Even on so-called "platinum" plugs, the ground electrode is usually a
nickel alloy, while only the center electrode is platinum. ( That's why it's
the  tiny one; platinum is costly.)  I only know of one plug that uses
platinum on the ground (outer) electrode and that is only on a tiny "pad" of
the precious metal (marketing gimmick, in my opinion).
 A spark doesn't know what metal it discharges from or to, nor does it care.
A spark is a spark, governed only by voltage and voltage rise, neither of
which is spark-plug-controlled.  The only thing (besides gap size) on a plug
that will affect a spark is the 'edges' on the electrodes.  A spark will
jump between two sharp edges more easily than between two radiused or flat
surfaces.  This means that it requires less voltage to spark over the same
gap with nice, new edges...and a marginal ignition system may find it easier
to fire this plug than an old, worn, rounded-electrode plug.
 A platinum plug's platinum electrode will last longer than the nickel
center electrode on a non-platinum plug (thus longer plug life).  The reason
that platinum is not generally used on the ground electrode is that the
center electrode errodes at a far greater rate than the ground electrode so
its not needed.
  This is not my speculation, this is stuff I've learned over the years from
sources I've found to be reliable, such as the spark plug manufacturers.
Feel free to do with this information as you see fit.
(and I know some of you will scoff simply because it comes from me...:o )
Larry




> ok, heres the general deal with plugs:
> copper plugs give you a better spark than platinum. think about it. you
dont
> see fance quad electrode copper plugs do you? reason is simple, its just
not
> needed with a copper plug. platinums do in fact last longer than copper,
but
> have to do crazy tricks to try and get the spark equivalent to a copper
> plug. here are the basic trade-offs:
> copper:
> adv: conducts better at its surface
> dis: breaks down easily - lower life
> platinum:
> adv: lasts extremely long
> dis: usually very small platinum electrode surface area, and also doesnt
arc
> as well as copper
>
> i tried the bosch super +4 plugs in the rieger once. after one day of
> driving i ended up changing back to coppers and noticed an improvement.
the
> only catch is that the 'improvement' only lasts for 3-5 k miles, then the
> plug acts like a platinum plug.
>
> general rule:
> if you suck at maintenance on your rocco, get platinums, they will likely
> outlast your engine.
> if you can remember to change them out regularly, go with coppers, you
will
> be rewarded every time you change them out.
>
> all of this is of course IMO, but i've got a decent amount of experience
> with these things.
> Al