re: Bosch plat+4 EC article

["Matt Martinsen" <mattmartinsen@hotmail.com>]

Per request I'm going to briefly summarize the Feb. EC article.  
It seems the main advantage is long life, 100K miles, in accordance with 
stricter emission laws determining the longevity of critical emission 
components.  This long life is in part due to the four prongs, it keeps 
a nominal gap longer because as the closest gap is widened by wear, a 
different prong would take the spark. The exotic yttrium alloy mentioned 
by another lister also greatly contributes to long life. Another 
characteristic is the side gap, or what Bosch terms surface gap.  This 
exhibits better self-cleaning properties than traditional air gap (prong 
sticking over the top of the electrode) plug. The plug will also fire at 
lower voltages, this would be a benefit for weak ignition systems and 
could be a benefit for turbocharged engines as higher boost levels make 
it more difficult to achieve a spark.  If the plug already took less 
voltage to spark, high boost pressure would be less likely to quench the 
spark.  At the time of the article, there were no turbo applications 
because Bosch was releasing the plugs first in applications they knew 
would work, for more difficult (turbo) applications with colder plugs 
they were going to do more testing and then release the plugs.  No 
inherent problems with using them in turbos, just a bit more difficult 
to design and dial in due to the extremes in a turbo engine of lean, off 
boost running and rich, high boost operation.  Both the enhanced 
cleaning properties and lower voltage spark initiation would seem ideal 
for turbo vehicles.
This is how I interpreted the article.  I'm just the messenger, I really 
don't know any more about plugs than the next guy.
-Matt Martinsen
Seattle, WA
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