[s-cars] let's talk about spark plugs

[Mike Fitton]

I'll use this as my starting point:  I'd really prefer not to pay 
$13/plug if I can help it.  That said, I will if I have to.

Okay, the stock plug is the F5DPOR.  Bosch's platinum plugs are never 
cheap.  I remember dealing with this several years ago when I had a 
Corrado G60.  That engine is extremely sensitive to plug choice.  The 
plug for that car, IIRC, was the W6DPO, also at around $13 each.  
Conveniently, Bosch also makes a W6DC, which is identical except that 
it's copper instead of platinum.  Copper conducts better, but doesn't 
last as long.  At $2 each, this wasn't a big deal.  You have to replace 
the plugs every 20k miles or so, but the PG engine is known for eating 
plugs no matter what.  W6DPOs do well to last 60k.  For a comparison, 
the guy I bought it from had installed F6DTCs, which I believe were 
appropriate for those 16v CIS I4s (RD?), shortly before I bought the 
car.  They lasted about 1k into my ownership, and I drove the GTI for a 
few weeks while I figured all this out.

Bosch doesn't, however, make an F5DCR.  Three minutes of diligent 
searching has revealed that Advance has a few NGK plugs for the AAN 
application, and I recall some NGK being the only real alternative to 
the W6Dx plugs that would last more than a month.  So my extremely 
limited opinion of NGK has since been a little higher than all the other 
retail plugs.

I think the AAN is equally sensitive to plug choice as the PG, but for 
different reasons.  I'm mostly worried about plug choice affecting the 
rest of the ignition system.  In my head, a copper plug has less 
resistance and will make the coils and stuff last longer.  On the other 
hand, sometimes the way it works in my head has nothing to do with the 
way it works in my engine.  The NGK plugs also have a 7 in the model 
number rather than a 5.  Maybe they just measure heat ranges 
differently?  I dunno.  I'm not completely fluent on all the impacts of 
adjusting the heat range, so I'm not prepared to adjust that without 
knowing exactly what I'm doing.  On the other hand, I would very much 
like to move to a copper plug because they'll definitely be cheaper and 
maybe they'll make everything else last longer.

Okay...discuss.

-Cheers!
Mike