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Platinum & Iridium Spark Plugs
Long-life spark plugs by ACDelco, Autolite, Bosch, Champion, NGK and Split-Fire all have platinum or platinum-tipped electrodes. With a couple of exceptions, most of these plugs use a conventional electrode configuration with a small platinum plug welded to the tip of one or both electrodes. ACDelco also offers a platinum version of its "Rapidfire" plug that features a fluted center electrode for improved ignition reliability. Likewise, Split-Fire offers a platinum version of its split electrode plugs for motorists who want extended life as well as reduced misfiring.

Bosch, who introduced the first platinum plug back in 1985, offers several different electrode configurations in their product line. Their standard platinum plug has a thin pure platinum center electrode with a single yttrium-alloy end electrode. Their Platinum+2 and Platinum+4 plugs, on the other hand, have a unique "surface gap" side electrode design with two side electrodes on the Platinum+2 plug and four on the Platinum+4 - a sort of good, better, best approach to platinum plug technology. Increasing the number of side electrodes gives the spark more paths to ground and reduces the risk of misfire, while extending plug life by spreading wear over more electrode surfaces.

In the fall of 2006, Bosch introduced yet another long-life spark plug called Platinum IR Fusion. Similar in design to the Platinum+4 plug, this new plug uses a center electrode made of a unique iridium/platinum alloy. The four side electrodes are a wear-resistant yttrium alloy. By combining platinum and iridium in the center electrode, Bosch says their new plug provides even longer service life (probably the longest of any spark plug that is currently available). Bosch also says their new Platinum IR Fusion plugs are an ideal replacement for any engine that comes originally equipped with either iridium spark plugs or platinum spark plugs.

One important point to keep in mind with respect to Bosch Platinum IR Fusion, Platinum+4 and Platinum+2 plugs is that these plugs are pre-gapped at the factory to a uniform 1.6 mm setting and should not be re-gapped to the specifications for a standard spark plug. It's very difficult to get even spacing with multiple electrodes so install them without changing the electrode gaps.

 NGK "Iridium IX" and Denso brand "Iridium Power" plugs use a different exotic metal for their center electrode: you guessed it, iridium. Alloyed with rhodium, the iridium electrode is six times harder and eight times stronger than platinum. Pure iridium also has a melting temperature that is almost 1,200� F higher than platinum, making it a very tough metal indeed. On late-model Toyota and Lexus applications, the OEM-recommended replacement interval for Denso iridium plugs is 120,000 miles.

The iridium plugs also have a very thin (0.6 mm to 0.7 mm depending on the plug) center electrode. The end electrode has a "U-Groove" that improves ignition reliability and wear resistance. Denso says their design reduces the required firing voltage up to 5,000 volts compared to a standard spark plug.

For performance applications, Denso has also developed Iridium Power plugs with a super narrow 0.4 mm center electrode. These plugs are engineered to improve ignition reliability under extreme driving conditions rather than longevity, so the recommended replacement interval for the iridium plugs with the super narrow 0.4 mm center electrodes is 30,000 miles.

Here's another bit of trivia for the gray matter: Iridium is literally an out-of-this-world metal. Approximately 50 million years ago, according to the Denso website, a giant asteroid from outer space smashed into our planet near the Mexican town of Chicxulub in Yucatan. The impact created a firestorm and dust cloud that darkened the Earth for years, wiped out the dinosaurs and left us with a layer of iridium-rich deposits that is evenly spread across every continent (the "K/T boundary" layer).

People always ask my plug recommendations. I must say that I like the NGK V-Power Plugs, the Champion Premium Fine-Wire Gold plugs, and the Nippondenso U-Groove plugs for domestics. In the Imports, the Bosch or NGK Platinum plugs usually work best. I have been testing the AC RapidFire plugs currently and I must say I am impressed by the results. Plugs that are useless to me are the Split-Fire plugs (poor materials -- actually an Autolite plug with the "V" tip), and of course the Autolite plug itself. I have seen the most failures and poor performance out of these plugs. This is not a bash session, so those of you that love your Split-Fires or Autolites, I'll wait for you at the finish line  ...