Spark Plugs: What's Next After Platinum?, Larry Carley, Counterman, December 2000

Platinum is a buzzword today for durability - and for good reason. Platinum is one of the best conductors of heat and electricity. It also resists chemical corrosion and electrical erosion much better than steel alloys, making it an ideal material for the spark plug electrode(s). Some plugs have a solid platinum center electrode while others have a small button of platinum welded onto the tip of the center electrode or both electrodes (single platinum vs. double platinum).

The main reason for using platinum electrodes is to minimize electrode wear. Every time a plug fires, a tiny amount of metal is vaporized and lost from the surface of both electrodes. The center electrode typically suffers the most wear because it runs hotter than the side electrode.

As the electrodes wear, the air gap across which the spark must jump becomes wider and wider. The gap on a standard spark plug grows about 0.00063m. to 0.000126 in. for every 1,000 miles of normal driving. And the wider the gap, the greater the voltage needed to jump the gap. On standard plugs, the firing voltage requirements creep up about 500 volts for every 10,000 to 15,000 miles of driving. Eventually, the plug may need more volts to fire than the coil can produce, causing the plug to misfire.

Using platinum almost eliminates electrode wear. Platinum is expensive, but it can double or even triple a spark plug's normal service life - from 30,000 to 45,000 miles for a standard plug up to 60,000 to 100,000 miles or more with platinum. Most aftermarket plug suppliers do not make specific mileage claims for their platinum plugs, but say to follow the OEM replacement intervals - which in most cases is 100,000 miles for platinum plugs.

Though long-life platinum plugs cost more than standard spark plugs, the OEMs are using them for several reasons. One is that they reduce the risk of misfire, which is essential to meet OBD II requirements. Another is that they help prolong the life of the catalytic converter (also by reducing misfires). Third, they almost eliminate the need for periodic maintenance. On many engines today, replacing the spark plugs can be a difficult and time-consuming job - particularly the back bank of plugs on transverse-mounted V6 engines in front-wheel drive cars and minivans.

One important point to keep in mind about platinum plugs is that they're not all the same. Some are more durable than others, and some provide better fouling resistance and ignition performance than others. It all depends on the design of the plug, the type of alloys used for both the center and side electrode(s), the configuration of the electrodes and the engine application.

A variety of exotic alloys are used in electrodes to improve durability and performance. Bosch, for example, uses a nickel-yttrium alloy for the side electrodes in its "Platinum Plus 4" spark plugs. In Europe, Bosch has recently introduced a new plug that uses yttrium for both the center and ground electrodes. For years, Champion manufactured a premium plug with a gold-palladium center electrode and copper filled side electrode. Champion has discontinued their gold plug and is now offering a premium "Platinum Power" plug with a platinum tipped center electrode. Autolite uses a chromium-nickel alloy for the ground electrode with its platinum tipped center electrode plug, while ACDelco uses a silver-nickel alloy side electrode with its platinum tipped plugs.

Denso and NGK have both introduced new premium plugs with iridium alloy electrodes. NGK says iridium is even better than platinum in terms of corrosion, and resistance and ignition performance.

Many spark plugs today have unique electrode designs such as V-split, grooved or clipped ground electrodes, multiple ground electrodes, fluted center electrodes, V-notched center electrodes, etc. Though each plug manufacturer takes a slightly different approach and claims various benefits for their design, the basic idea is to make it as easy as possible for the spark to jump the gap and ignite the fuel mixture. A spark jumps more easily between small, sharp surfaces than large dull ones - which is another reason why new plugs require less firing voltage than old ones with worn, dull electrodes.

Another issue that plug manufacturers talk about is "unshrouding" the spark so it has a better opportunity to ignite the fuel mixture. Opening up the spark also means the flame kernel it creates can expand more rapidly and evenly inside the combustion chamber, reducing the chance of the flame kernel being quenched and a misfire occurring. Split-Fire's V-shaped ground electrode as well as Bosch's surface gap four electrode Platinum Plus 4 are both designs that claim to expose more of the spark to the fuel mixture.

One thing to keep in mind about all "performance" spark plug designs is that no plug can magically create horsepower out of thin air or add horsepower that wasn't there in the first place. But improved ignition reliability can minimize horsepower losses caused by misfires. That's why some plug manufacturers claim their spark plugs improve power. The gains come from power that was being lost to misfires.

Good plug wires are just as important to ignition performance as the spark plugs. The wires carry high voltage from the ignition coil to the spark plugs. Each wire has a conductive core surrounded by a layer of insulation. The insulation may be surrounded by additional reinforcement such as braided fiberglass and a protective outer covering or jacket. At both ends of the wire are terminals which connect to the spark plug and distributor cap (or coil pack in distributorless ignition systems). Each end also has a boot to keep out moisture and dirt. Spark plug boots are usually molded silicone rubber, but on many import applications are phenolic or metal tubes.

The type of insulation used in a plug wire is also important. Premium wire sets typically use silicone or EPDM (Ethylene Propylene Diene Monomer) insulation which offers higher temperature resistance than Hypalon or other materials. Some premium wire sets also have a protective outer covering of EVA (Ethylene Vinyl Acetate). EVA provides thermal protection to over 400 degrees and has a tensile strength 200 percent higher than silicone.