[s-cars] Which spark plugs

[Scott Justusson]

 Well, save yourself 22$ and just buy a copper plug if that is your presentation?  Any plug will work. I suggest you get a copy of the Denso Iridium White Paper (1999) to test some of your opinions and observations.  Audi calls the Service Interval of the F5DPOR to be 25k on the 20vt engimes/  I personally suspect that is to help reduce the amount of secondary voltage and dwell issues of a 7200rpm redline turbo engine.  Certainly if you are running a 20vt at 100k, you are risking spark issues, even at stock boost.  Will the engine *fire* that plug to 200k?  Ok, probably.

When I did this research years ago, the iridium High Performance .4 vs .7mm electrode was my plug of choice, my first swaps were to my 3B engines because the required secondary voltage published in the paper dropped 5kv.  Not as key as the AAN COP, but significant even with COP.  Add in a 50% better wear resistance and a 25% increase in temp resistance, the Platinum Plug really became obsolete in a turbo application 15 years ago.

Just about any turbo tuner regardless of marque, will use a HP Iridium Plug...  Or just copper.  I would say for a COP either is fine, because the 'flameout' issues in a copper just don't appear to be present with a COP application.  I'm a bit more reluctant to say the Copper is 'better' in a single coil application, but I routinely keep sets of copper plugs around to diagnose ignition problems in all 20vt engines.

I will further opin two things on the F5D,  If you use it, make sure you replace it at 25k - period.  The combustion temps those plugs are exposed to mean degredation and failure of the plug increases exponentially past this (Audi Factory) Service Interval.  Second, if you insist on using it, and lose an electrode, your best hope is it either burned up (unlikely) or it exited the chamber without damaging vital engine components.  

This isn't an oil thread or mountains of opinion...  Iridiums in non boosted applications are as overkill as an F5DPOR is.  However in the world of boost, especially high boost, ignoring the benefits of the iridium technology seems stubborn.  I say there are many reasons *not* to use the F5DPOR in the I520vt - stock, and especially, boost tweeked.

This thread has been bounced around a while, but it is not 'rumor' or opinion, I believe the bad rap the F5DPOR got is from the guys that work on more than 'just a couple'...  Because it doesn't take many experiences to ascribe that plug less than stellar.

Cheers, HTH and my .02

Scott J


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-----Original Message-----
From: Mike Miller <mikemilr at blackfoot.net>
To: s-car-list <s-car-list at audifans.com>
Sent: Sat, Mar 22, 2014 1:07 am
Subject: Re: [s-cars] Which spark plugs


I ran F5DP0R's in my 91 200q's without issue - swapped one set out after 
100k+ miles just because. They still looked good and ran fine.

In the current UrS6, running over 25psi boost, I'm using FR5DTC which 
seem to be doing OK. Not a lot of miles on them yet - maybe 5k.

--mike

On 3/21/2014 10:21 PM, Scott Justusson wrote:
> Er, ok add me to the list of those *not* using FD5POR *ever* again, because 
when I had my shop, I have seen too many fail from the box, blow a pin hole in 
the ceramic and or just lose the electrode all together on high boost.  I had 
really good luck with NGK Iridiums for a while, but have recently just been 
content with a plain old Porsche Turbo app triple copper plug.
>
> FYI, that FD5 is supposed to have a 25k service interval in a stock 20vt 
engine, so beyond 30k (IME) you are asking for coil pack issues from a 
resistance problem.  I know I am not the exception to the opin that the FD5POR 
is hardly first prize at the spark plug county fair.  Bet you won't find m-any 
I5 tuners using that plug.  Lose and electrode once, you won't swear *by* them 
ever again.
>
> Just sayin
>
> Scott J
> 7 x 20vt engines = 0 x FD5POR equipped
>
>