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Spark Plugs, light my fire!
Spark plugs are a pretty basic maintenance item in most cars but with turbocharged cars, especially those making higher than stock levels of power, spark plugs become a vital part of the power delivery system. Additional tune up items typically include cap/rotor and spark plug wires but spark plugs take the brunt of the wear in the ignition and it’s not uncommon to have to replace them 3-4 times before any other ignition systems components require attention. With that said let’s look at the options out there and the benefits of each.
Copper plugs: Whether Bosch, NGK, or otherwise the copper plug is hard to beat for many applications. OE equipped for non turbo cars and commonly used in turbo cars as well even though the OE called for platinum in many cases. Copper does have a lower melting point than other metals like platinum or iridium but for inexpensive replacement cost and consistent performance they are hard to beat. For a higher HP turbo car expect to get 20-25K when using these plugs.
Platinum plugs: OE equipped in most turbo applications (Volvo) these plugs do quite well for cars that are younger and have fewer miles. However for models that are upwards of 80K on the odometer these might not be the best choice depending on exactly which units you get. See the images below.
Note the Bosch Platinum plug on the left and pay close attention to the electrode in the center of the plug and how shrouded it is by the insulator. Now contrast that to the standard copper plug on the right and you can start to see how much more open that electrode is. For younger, cleaner burning motors this typically isn’t an issue but as an engine ages and more oil starts passing through the intake system from additional blow by and reduced PCV system performance that can lead to deposits that form on the plug and can intrude on spark ionization across the electrode to the ground strap. This is why some folks have switched to copper plugs even in the turbo engine. There are however Platinum plugs available that have a fully exposed electrode so that becomes the best of both worlds as Platinum plugs in that iteration have the best performance and longevity as compared to copper.
Iridium: Iridium plugs came on the scene a while ago and were immediately boasted as near-magical in their capability. While they are certainly an improvement in spark plug technology they are after all just regular spark plugs with updated materials and design. The main benefit of these plugs is two-fold.
- First the iridium material used in the electrode is rated for a higher temperature range of operation and greater resistance to corrosion from combustion chamber gasses.
- Secondly the electrode in the iridium plugs tends to be much smaller as the material can handle higher temps without melting away, the smaller center electrode promotes more consistent spark jump as spark ionization has the best chance of occurring when the spark jumps from a sharp edge.
The spark plug on the left exhibits the rounded center electrode that has worn over time while the spark plug on the right shows the appearance of a brand new electrode that has nice crisp edge for the spark to jump from. This is the nature of why a spark plug wears out from both center electrode wear and ground strap wear.
The latest: For the higher HP cars we’ve been building we’ve had the greatest success with Bosch motorsports plugs. They are an iridium platinum hybrid which in and of itself isn’t tremendously special but there is a very unique design element to them which makes them desirable for the performance enthusiast. Note the picture below:
The center electrode is reduced in size, again due to the nature of iridium to withstand the higher heat without melting away, but the ground strap has been redesigned to not only provide a more pointed tip but also has been pulled down and to the side of the center electrode which reduced flame front propagation in the cylinders as the combustion is initiated. These plugs are what we’ve been seeing the best results from as of late and it’s what I recommend to anyone who’s been having ignition system issues they can’t seem to solve. While they’re not magic they are well built and designed which means for you and me we literally get the best bang for our buck!
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Robert Lucky Arnold
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