| little comparison of the zfr6f-11 extended tip electrode plug vs. the stock pfr plugs. installed each plug into a tt head and measured from the cylinder/deck surface to top of plug, both with same gap. they are very close maybe .250mm shorter with the copper plugs if that. they are both a little over 5mm above the deck surface. the copper plugs do not have the extended section after the threads, wich does expose the ceramic material more to combustion. seems to me this would benefit in taking a little more heat out of the cylinder as well. 
stock pfr6b-11b left, zfr6f-11 right
just thought some of you might be interested, since there is such a anti-anything that is not stock when it comes to plugs on here. i personally run the these plugs and they actually seem to make my car run/idle better, and i do not have to gap them as tight as i do with the pfr plugs at the same boost level. they are also 1.98$/per plug here at the local advance autoparts the only downside i can see with them is they do not last anywhere near as long as the stock plugs, i personally have not pushed them past 5k miles. but for 1.98$ a pop it doesnt bother me to replace them frequently, aslo gives me a chance to read the plugs anyway.
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ngk copper (zfr6f-11) vs. stock (pfr5b or 6b-11b) - 
