These plugs should provide the firing characteristics of copper, but last as long as platinum. I got these on a previous car, and I think I noticed slightly better throttle response, but that was the old unreliable butt dyno.
On the Duratec v6's, you should stick to the stock Motorcraft/Autolite Dual platinum plugs...anything else and the Duratec eats them like candy. Everybody that uses anything else expeiences the misfires and stumbling from worn plugs in as little as 4k miles. If you're expecting a HP boost from spark plugs, forget it. Plugs will make *virtually* no horsepower. Save your money on these and put it toward a more worthwhile mod.
Duratecs fire the plugs on the rear bank from ground to electrode as ppposed to the normal electrode to ground firing...because of this, the metals on the firing ground on the rear bank will melt/wear very easily on a plug that doesn't have the platinum on the ground electrode...hence the need to DUAL-platinums. The iridiums would work fine if they were Dual-iridium, but they're not .
For evidence of this, search the Duratec Performance forum over at contour.org
A few quotes:
"Well for what its worth..I recently had my ECU reflashed by 2 ex-Ford guys with 20+ combined years in the ford ECU tuning buisness (with dyno correlation for each tune) and the subject came up from a Cobra guy. What these guys said was that on an N/A/no nitrous car with streetable lvl compression they have never seen a plug gain more than OEM Ford plugs or autolites. And in many cases, power loss was evident.
"The Denso Iridiums have a nickel plated Ground Electrode and since a small % of the current goes through the ground, without a platinum cap, the metal will not last long. In my test the plugs performed astonishing for about 6kmiles before I started to notice a slight decrease in performance. After looking at the plugs I than knew why? Denso does make a Iridium Racing Plug that I wanted to put on my car, there $55 per plug, but they have a number of added features over the regular iridums and has a platinum cap on the Ground Electrode. Unfortunately these plugs are a gasket type and so will not work on our cars."
Different plugs work wonders in different engines...My turbo thunderbird does best with bottom of the line copper plugs, this plug may be great in the IS300, but the Duratec does best with the stock Autolite Dual-platinums,