Quote Originally Posted by wetamup2k3g View Post
Some people may know this, some may not, but platinums and iridiums are used for their resistance to corrosion and thermal breakdown, not so much because they are better conductors than copper. Higher than normal combustion temps or a stronger spark delivery system may require the use of more exotic spark plugs, but if your stock motor doesn't call for them, don't use them, their is no real benefit.

From what I was told in school, most non-high-performance cars use platinum plugs simply to lengthen service intervals, as the platinum doesn't degrade as quickly as copper plugs. In fact, platinum is not as good a conductor as copper, so a given spark would see more electrical resistance going through a platinum plug than it would going through a copper one of the same build, meaning the spark from the copper one is stronger. This could possibly explain the constant misfiring I had going on in my 4-cyl when I ran platinums in it that one day (put them in, and took them right back out).

However, a copper plug wouldn't be able to handle the heat and pressure a platinum or iridium plug would be able to in high-performance applications, which is why they are used.

This is all anecdotal info, but from what I know about conductors, it makes sense. Hope this helps out.
yes, this is the reason mitsu uses platinum plugs in the v6: to extend service life. the spark plug change on v6's is not as simple procedure as on some other configurations, due to the intake plenum covering the entire rear bank of 3 cylinders on our v6's. it's not a very hard service but is significantly more involved and time consuming as compared to the i4 engine, because to access those 3 plugs, the plenum has to be removed.