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Iridium IX spark plugs: Boosting special engines with a precious metal upgrade

From their platinum beginnings, precious metal spark plugs have been around for more than 30 years. Today’s highly advanced iridium electrodes offer the optimum combination of sparking performance and long life. World-leading ignition and sensor specialist NGK SPARK PLUG explains how its Iridium IX range has made yet another quantum leap in spark plug technology for a range of engines.

Motorcycle riders, classic car drivers and boat owners may favour different forms of transport, but they all want the same, reliable start and thousands of kilometres of trouble-free travel. That was the concept behind NGK SPARK PLUG’s introduction of Iridium IX: to make the highest performance, modern Iridium technology spark plug upgrade available to the Aftermarket – including vintage motorcycles and cars which did not have Iridium technology fitted ex-works, because it did not exist at the time.

Power for 2-wheels

Recognising particular demand for upgrades from the 2-wheel sector, the company initially launched its Iridium IX technology in 2006, especially for motorcycles.

The goal, explains Kai Wilschrei, Senior Manager Technical Services Aftermarket EMEA at NGK SPARK PLUG EUROPE, was to help riders achieve significantly better performance from their bikes, whether on the road or track. “Motorcycles are often fitted with standard nickel spark plugs as original equipment. But the extreme strength and durability of iridium offers the potential for enhanced ignition reliability and performance. With Iridium IX – short for ‘Iridium IXtreme’ – we were able to give riders improved ignitability that lasted even longer than platinum. They could also enjoy a smoother, more economical riding experience.”
To create the new technology, NGK SPARK PLUG engineers designed an ultra-fine, 0.6mm diameter iridium alloy tip, laser welded onto the plug’s central electrode. Together the slimmer iridium centre electrode and taper-cut ground electrode kept the required ignition voltage low and put less stress on the ignition coil, whilst generating a powerful spark. In addition, the consistent distance maintained between the hard-wearing electrodes avoided misfires. “We also devised an anti-fouling annular gap to make sooting a thing of the past,” continues Wilschrei. “This made cold starts problem-free and gave the best ever performance in stop-start traffic, where motorcycles need to excel.”

A positive side-effect of the innovative material was Iridium’s impact on spark plug lifespan. The expert adds: “Iridium is one of the world’s most durable metals: around six times harder than platinum. Added to its very high melting point of 2,450oC, it’s extremely resistant to spark erosion. As a result, the lifespan of the iridium electrodes in our IX spark plugs is significantly longer compared to the electrodes of conventional nickel plugs. That’s worth the investment for any rider whose motorcycle isn’t already fitted with original iridium plugs.”

Iridising vintage cars

The benefits of Iridium IX are not restricted to 2-wheels. NGK SPARK PLUG soon expanded the technology to put more power under the bonnet of classic cars too.

“Iridium IX offers an excellent upgrade opportunity for older cars and some younger ones, as well” affirms Kai Wilschrei. “Fitting them as replacement spark plugs assures vintage car drivers of reliable first-time ignition, no misfires and the longest possible service life – with no carbon build-up.”

Wilschrei himself owns a vintage Audi 90 built in 1985, as well as an old scooter. “The first thing I had done after buying the car was to replace the spark plugs with Iridium IX upgrades,” he confirms. “Now the car is much quieter when the engine is idle. Starting performance is also very good. The same goes for my Vespa!”

What riders said

When NGK Iridium IX spark plugs were first launched, more than 230 riders of modern and classic motorcycles tested them out. Here is some of their feedback:

- “The Iridium plug has optimised the running smoothness of my single cylinder.” Rico

- “After five refuelling cycles the plug has already paid for itself. Fuel consumption has dropped to less than five litres per 100 km.” Kirsten

- “The Iridium plug changes driving and response behaviour significantly. What I like most is that the power kick-starts about 1,000 rpm earlier, which is very useful after cornering.” Andre

- “There has been a clear difference to normal spark plugs, especially in winter. Starting behaviour was clearly better and even with a cold engine its smoothness was remarkable.” Othmar

More life on the waves

The Iridium IX effect can also be enjoyed on the water. The high-tech plugs offer workshops and boat owners a simple way to boost the performance of almost every marine engine. “Because the electrode design of Iridium IX plugs reduces the voltage needed for a powerful spark and extends plug life, they are ideal for use on the sea or inland waters. Boat engines start more easily, run better and accelerate more smoothly,” advises the expert.

The advantages aren’t just for high speed trips. Iridium IX spark plugs also improve response at the slower pace of canal narrowboats, on floodplains and moving around harbours or marinas. This is because the anti-fouling annular gap prevents the sooty deposits that often accumulate on nickel marine plugs at low speeds.

“NGK Iridium IX upgrades deliver first-class performance, efficiency and reliability for motorcycles, classic cars and boats, whether in motorsports or on everyday journeys,” concludes Kai Wilschrei. “Everyone should make the move!”

To find out more about NGK SPARK PLUG’s Iridium IX spark plugs visit

Technology insight

Fitting Iridium IX spark plugs offers end-customers a host of advantages:

- Improved ignition: 0.6mm diameter iridium tip focuses electrical energy around the centre electrode, producing more efficient air-fuel ignition

- Faster starting; quieter running: High ignitability means the engine starts up quickly and runs smoothly, even on cold, damp mornings. Hydrocarbon emissions also reduced

- Better fuel consumption: More ignitable mixture reaches the spark, increasing combustion efficiency and reducing fuel use (In 2-wheel test: 5.64 litres used/100 km with 2.5mm standard plug, vs 5.55 litres used/100 km with Iridium IX)

- Longer  lifespan: High melting point means iridium centre electrode lasts longer  than standard plug electrodes

- Fewer misfires: Standard spark plugs gradually erode, increasing the distance between electrodes, affecting ignition quality and causing misfires. Consistent Iridium IX electrode distance avoids these issues

- No carbon build-up:  Special annular gap prevents the carbon particle deposits that can block ignition voltage: especially beneficial in stop-start traffic



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