Originally Posted by RDY4WAR
Originally Posted by MolaKule
Originally Posted by RDY4WAR
This topic is fascinating to me, and sorta relevant. I've recently tried fine wire iridium (NGK TR5IX and TR55IX) plugs in my track car. However, it didn't like them at all. Above about 5500 rpm, spark blow-out (I'm assuming that's what is going on) was common and mis-fires frequent. This happened at both .060" and .040" gaps. It was less frequent at the narrower gap, but still present. However, I went back to conventional nickel alloy V-groove plugs and even at .060" gap, it runs flawlessly with no misfires. I'm not complaining as the nickel plugs are considerably cheaper, but perplexed as to why that would be the case. This is a rather mild, naturally aspirated drag race application with coolant temps in the 160-180°F range.
This may answer your question as to why your V-groove plugs performed better:
http://www.ngk-sparkplugs.jp/english/techinfo/qa/q09/index.html
I understand that, but I'm not following why that made it perform better than a fine wire. Wouldn't a fine wire tip be even better at that?
Let's examine why misfires might happen (which is what I am assuming happened in your vehicle and assuming your spark energy capability was sufficient), just thinking out load for a moment:
1) High pressure exceeds spark energy capability, (i.e, not enough spark energy to overcome
pressure as per Paschen's Law),
2) Mixture too rich for spark energy to overcome fuel/air ratio (stoichiometry related - not enough spark energy to overcome
rich gas mixture as per Paschen's Law)
3) Turbulence in combustion chamber extinguishing or impeding expanding plasma outside core plasma,
4) Spark knock sensor retarding spark timing (possibly sensing preignition due to carbon deposits and not enough spark energy to overcome
gas Temperature as per Paschen's Law),
There may be others but I think the V-groove geometry has to do with #3. "The flame core is generated near the perimeter of the electrodes and grows" and "Ignitability is improved because the electrodes are interfering less with the growth of the flame core."
I.e, you have two flame cores at two fine points rather than one expanding out in what I assume is a Figure 8 pattern and meeting at their edges to enhance the compression wave.
Anyway, that's my hypothesis.