Although the spark plug has existed for over 150 years, things have definitely changed over the past century and a half. The modern, high voltage spark plug, which was invented by an engineer at Robert Bosch in 1902, was actually invented merely as a by-product of the magneto-based ignition system. While the magneto-based ignition system no longer exists today, the spark plug lives on as a critical part in many of today’s internal combustion engines.
Until the late 1970s, the central electrode of essentially all spark plugs was composed of a nickel alloy. With new developments in engine performance, the standard nickel alloys were no longer able to meet the requirements of new engines of the day. Nickel alloys could not simultaneously be “hot” enough to burn off the carbon deposits left by urban driving and “cold” enough to withstand extended high-speed travel on highways. Copper was chosen as the metal to solve the problem, with a nickel-chromium coating around it to improve durability.
Copper-cored spark plugs were the standard until the mid to late 1990s, when platinum spark plugs began to rise in popularity as both original equipment and aftermarket upgrades. Bosch was a pioneer in the use of platinum in its electrodes, first developing a platinum-tipped spark plug followed by a spark plug with both a platinum tip and four electrodes. A common misconception about platinum spark plugs is that platinum is used because it possesses a higher electrical conductivity than copper; however, this is not the case. Platinum does not conduct electricity as well as copper, but it is much more durable and is therefore able to be formed into much finer tips than copper.
The advancement of platinum was followed by laser welding of the tips. This new process helped to ensure consistency, durability, and precision in the spark plug manufacturing process. However, it also added significant cost, which was reflected in the increased purchase price to the consumer. NGK was the first to introduce laser welding of the tips, but many other manufacturers have also adopted this technology.
After platinum tips came iridium tips, also pioneered by NGK. Iridium provided the strength advantages of platinum, but with much better electrical conductivity than platinum. Laser welding of the iridium tips was also implemented by NGK. In the ongoing battle to produce the best spark plug, Bosch replied by introducing an iridium tip and a tapered ground electrode with a laser-welded, iridium-platinum alloy inlay, instead of the usual high nickel steel electrode. Bosch also introduced continuous laser welding in their manufacturing process, producing an even stronger and more durable weld than NGK’s pulse laser welding process. Bosch supported (and continue to support) their performance claims by offering a 7 year performance guarantee, an unprecedented warranty in the spark plug market.
Choosing the best spark plug for your vehicle
There is a large body of personal opinion that exists in the spark plug market. Many older “car guys” swear by the American brands of old, such as Champion for Chryslers and AC Delco for GMs, claiming that their vehicles will not work properly without these brands. This could not be further from the truth, especially considering that many of the foreign spark plug manufacturers have found their way into a wide range of North American vehicles (but not vice versa).
Bosch and NGK iridium plugs tend to be the best performing plugs on the market, but they are not really worthwhile on older vehicles. A good platinum plug or maybe even just the standard copper plug will yield the best results in regards to performance and durability. In newer vehicles, iridium plugs are the way to go, giving better performance and durability than any other plugs on the market. Although platinum and iridium plugs may be more expensive up front, there extended service lives help to offset their higher initial price. The recommended change interval for a copper plug is around 30,000 km (18,600 miles), while platinum has a change interval of 100,000 km (60,000 miles) and iridium a change interval of 120,000 – 190,000 km (75,000 – 118,000 miles). Also, when changing plugs, be sure to replace your plugs with new plugs of an equivalent or better metal. Never downgrade (e.g. replacing platinum original equipment plugs with copper plugs), as this will likely have a negative effect on both vehicle performance and gas mileage.