Miata Mailing List: November 1992, Message #24
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   From: (none)
Subject: Re: Platinum plugs
   Date: (none)

Regarding Platinum Plugs

I used platinum plugs on my 90 model and did not notice any improvement or 
detriment to performance.  

The Winter 1991 issue of Miata Magazine has a brief article on page 46.  It 
says that platinum plugs will not help performance because the Miata has two 
ignition coils.  Each plug fires once *every* revolution instead of every 
other revolution.  This is also why unless you use a jumper in the diagnostic 
connector, your timing light will flash twice as much as needed to hit the 
mark.  

The article says that the current will flow down one plug and back up the 
other.  Two plugs always fire at the same time.  Since platinum plug 
manufacturers only plate the center electrode, two of the spark plugs will 
have the current flowing the wrong way negating any benefit.  

It goes on to talk about current flowing from negative to positive and so 
forth.  Down one and up four, down two and up three.  This is all confusing to
me so maybe there is an electrical engineer out there who can better explain 
it to us all.  All I know is that I use split fire plugs and have noticed a 3%
improvement in gas mileage and better performance.  They cost more, but so do 
platinums.