Iridium Spark Plugs | Advice & Information

Iridium is an extremely hard metallic element, related to platinum, which is thought to occur on earth primarily due to an enormous meteor impact millions of years ago. Other than it's hardness, the main property which makes Iridium attractive as an electrode material for spark plugs is its extremely high melting point (almost 2,500 deg C).

Since late in the 20th century Iridium has been used in alloy form as material of choice for construction of Spark plug and industrial igniter electrodes. Pure Iridium is difficult to work with, very brittle and does not have great electrical conductivity hence alloys are used to give the best combination of these properties. An Iridium alloy electrode is able to deliver good conductivity and extreme hardness. The result is that an Iridium electrode can be manufactured with an extremely small diameter, when compared to a traditional copper or even a platinum tipped electrode, without compromising the useful life of the electrode or spark plug. The narrow diameter concentrates the electrical charge and therefore a much lower voltage is required to jump the spark gap. This is beneficial in several ways:

A lower voltage is required, this reduces load on a vehicle's ignition system (less strain = less chance of failure)
A larger gap can be supported without increasing load on the ignition system (Larger gap = larger spark = more efficient combustion)
A more precise spark every time, delivered in the correct position and with the correct timing (More efficient combustion)
Assuming a suitable Iridium plug is available, benefits you are most likely to see are:

  • Improved throttle response
  • Improved economy (though this depends largely on how much you enjoy the improved throttle response!)
  • Increased plug service life (Depending on design, an Iridium plug could last up to ten times the life of a standard plug with little reduction in efficiency over the plug's lifespan)
  • Increased engine power (Don't expect to double your horsepower but a 1 - 3% increase is possible)
  • Improved (reduced) emissions.

Will an Iridium spark plug be beneficial for my particular engine?

This is very subjective. The vast majority of vehicles/engines will benefit from replacing a standard spark plug with an Iridium spark plug. Most benefit will result if:

  • There is a very close Iridium spark plug match for your standard spark plug (i.e. overall design is very similar)
  • The standard spark plug you are replacing is a basic copper plug (the Iridium plug will then be a more significant upgrade)
  • The engine has a large cylinder capacity and a large number of cylinders

Least benefit will be realized if:

  • There is no close match for your standard spark plug, it isn't worth compromising plug design purely to use an Iridium plug type.
  • The standard plugs are already a performance or enhanced design. Some standard (Original Equipment) plugs are Iridium or fine wire platinum types, these may already provide the ultimate performance and service life for your particular engine. Fitting an aftermarket Iridium plug may actually result in a drop in performance and service life.

Denso Iridium Spark Plug types

Denso Iridium Tough Plugs

Denso's Tough Plug design combines an ultra fine 0.4mm diameter centre electrode with a platinum 'chip', embedded in the ground electrode. High quality materials are use throughout. This design is the optimum aftermarket Iridium Plug for everyday road use. Service life is around double that of the Iridium Power type without compromising performance. Service life of over 60,000 miles is achievable for normally aspirated engines. These plugs are a great investment for modern engines where performance is an issue and considerable time is required to service or replace the plugs. We keep all popular parts in stock as well as some less commonly requested designs. The correct part for your vehicle can be identified by using our 'Advanced Search' application.

Denso Iridium Power Plugs

This is Denso's 'basic' performance Iridium spark plug range. Tried and trusted by performance enthusiasts worldwide. A traditional ground electrode is teamed with Denso's ultra fine 0.4mm Iridium alloy centre electrode to provide excellent performance. Service life for normally aspirated engines can be up to 30,000 miles but we would expect plugs to be past their best by this time, 20,000 miles is a more practical target and replacing after a shorter interval may provide greater savings in fuel economy.

There are a wide variety of designs and heat ranges from 14 (very warm) to 34 (extremely cold) in some designs. We keep the vast majority of designs and heat ranges in stock.

Denso Iridium Racing Plugs

The ultimate protection for a race or high revving engines. Denso's ultra fine 0.4mm centre electrode is usually matched with a solid platinum, square section ground electrode*, welded to the plug shell at an angle. Vibration can cause issues with ignition systems in racing engines which may rev to 20,000rpm or more. The strength of these plugs ensures that vibration does not cause any issues and the chances of plugs fracturing or melting are greatly reduced.

Supplied in an individual, protective plastic case. We keep the most commonly requested plugs for cars and bikes in stock, others are available to order.

*Note that some race parts do not have a traditional ground electrode, these are known as surface discharge plugs and remove the risk of damage to the ground electrode (as there isn't one!)

Denso OE Iridium Plugs

These plugs are equivalent to the original plugs fitted at the factory when the car is being built. Usually a 0.6mm Iridium alloy centre electrode matched to a platinum chipped ground electrode for optimum service life without compromising performance. Service life can be as much as 120,000 miles for this plug type. Denso makes the OE parts for many vehicle manufacturers and therefore their aftermarket OE Iridium plugs are the best option to replace the original factory fitted plugs (where available). If a Denso OE Iridium plug is fitted as standard we would not recommend fitting any alternative part (unless the engine is heavily modified). Most OE Iridium plugs are available from stock.

NGK Iridium Plug Types

NGK Iridium IX Plugs

NGK's basic aftermarket Iridium spark plug range, though some part numbers are recommended as standard by NGK UK. A traditional ground electrode and a 0.6mm Iridium alloy centre electrode result in an Iridium plug which offers good value for money. Though not as performance orientated as Denso's Iridium Power, Tough or Racing plugs, the IX range does provide an extended service life and improved performance over standard copper plug types. You can find a suitable Iridium IX plug by using our 'Advanced Search' application.

NGK Iridium IX spark plugs

Not all NGK racing plugs incorporate an Iridium centre electrode. Those that do will have either a standard ground electrode design, usually in nickel alloy, or a solid platinum bar ground (similar to the Denso racing design) and a 0.4mm Iridium alloy centre electrode. Like the Denso Iridium racing plugs, these parts are designed for strength whilst maintaining optimum performance. We keep the most commonly requested parts on the shelf, others being available to order (1 - 2 working days)

NGK Laserline Iridium LPG Plugs

Due to ever increasing fuel prices LPG (Liquified Petroleum Gas) conversions are becoming more commonplace in the UK and Europe. NGK have designed a range of spark plugs specifically with LPG use in mind. Part numbers range from LPG1 - LPG8, these eight different designs cover the vast majority of petrol engined vehicles in the UK and Europe. A fine Iridium centre electrode and an embedded platinum chip in the ground electrode add to the performance and service life. The use of high grade materials (superior to those of standard spark plugs) prevents contamination, abnormal erosion and wear. Initial investment cost is high but overall costs are reduced due to the extended plug service life and improved fuel economy. We keep the entire LPG range in stock.

NGK OE Iridium Plug Types

NGK manufacture OE Iridium plugs for many major motor manufacturers. Design is usually a 0.6mm diameter centre electrode and a platinum chipped ground electrode. As with Denso OE, we would not suggest or recommend replacing an OE Iridium plug with an aftermarket equivalent, design would inevitably be slightly different and this will most likely have a negative impact on ignition efficiency. We keep a good inventory of NGK OE Iridium plugs in stock at all times.

Champion Iridium Plug Types

Champion OE Automotive Iridium Plugs

Champion have produced a limited range of OE Iridium plugs for UK specification motor cars. The same applies to Champion OE Iridium plugs as to Denso and NGK OE Iridium, if it's fitted as standard we wouldn't suggest changing it. These plugs are designed to be the ideal part for a specific engine and therefore they are unlikely to be suitable for any application other than that for which they were designed. Some parts are kept in stock, others are available to order.

Champion Industrial Iridium Plugs

Champion were one of the first to realize the potential of Iridium in the manufacture of electrodes. Iridium is the ideal material for use in Industrial ignitor electrodes. The combustion conditions in engines and generators running on natural gas, methane etc are extremely harsh, wear of plugs can be extremely rapid, engines often run 24/7 and servicing is costly. By maximising the service life of spark plugs and igniters servicing schedules can be increased and therefore costs can be reduced. Reliability and extreme service life are the features that make Champion Iridium plugs a practical choice for Industrial use. Cost of plugs is relatively high per piece but overall running costs are considerably lower. Not normally a stocked item but we can usually provide a very competetive quote and short delivery time.