RE: RE: spark plugs

["Osterbrink, Mark (AFS-Warren)" <Osterbrink@xxxxxxxxxxxxxx>]

I'll take a shot at answering the spark plug questions.   The purpose =
of
the plug is to ignite the air/fuel mixture.  If it is consistently
performing this task (as in most modern ignition systems in proper
repair), there is no extra power to be found from the spark.  If it is
not (as in many older points-type ignitions), some power may be gained
by increasing the spark voltage to insure consistent combustion of the
air/fuel charge.  NGK has a faq
(http://www.ngksparkplugs.com/Pages/faqs.html) that covers a lot of
these types of questions - I think someone from this list originally
pointed this faq out.  Some common misconceptions:

1)  A multi-electrode plug makes many sparks on each firing.  There is
only ONE spark for each firing of the plug.  The pictures in the adds
for these types of plugs are multi-exposures.  Once the air breaks down
and allows current to start flowing, it will all follow the past of
least resistance.

2)  More voltage produces a hotter spark.  The temperature of the arc =
is
fairly constant, and about 10,000=B0F.  Adding voltage increases the =
size
of the spark, but not its temperature.

3)  Producing a more "powerful" spark will increase an  engine's power
output.  The engine can't release any more energy than what is =
contained
in the charge trapped in the cylinder.  The spark ignites this mixture.
Once the spark is supplying enough energy to ignite the mixture and
allow the flame front to develop, adding more energy to the spark does
nothing (actually, adding more energy than required reduces power
because that energy has to come from somewhere, but this effect is
inconsequential).

In short, with a modern ignition system in good shape, you aren't going
to see an improvement from a higher voltage ignition system.  With an
older system, you may.  In my opinion, all of the "multi" spark plugs
are nothing more than marketing ploys, and will provide no quantifiable
benefit - but at least they won't damage your engine like some of the
snake-oil products.  The ultimate ignition system is probably the one
developed by SAAB that used the piston as the ground electrode - it =
made
some serious sparks at large advances.

------------------------------

End of bmw-digest V9 #550
*************************