Spark plugs are often overlooked, but are absolutely critical for peak performance. This PT guide will give you a good grounding in what can be a highly complex subject.
Getting a strong, clean spark in your engine’s combustion chambers is vital to get the most power in the most efficient manner, and with a modified engine the role of the humble spark plug becomes even more crucial. Spending a fortune on heads, pistons and cams can be a waste of time if you’re using worn plugs – or items inappropriate for the application. But these days there’s no excuse for using the wrong plug, and neither do you have to travel miles to get the correct one. The big names, such as Denso and NGK, along with Champion, offer plugs suited to high-performance applications, while various other specialist brands, such as Splitfire from the US, have plugs with a serious tuning pedigree.
IRIDIUM
A few years ago platinum was at the cutting edge of plug technology, but things have moved on rapidly. The current buzzword is iridium – Denso, NGK and Champion all offer iridium plugs.
According to Denso, iridium has major advantages for both performance and smoothness. At 0.4mm in diameter Denso’s alloy central electrode is the smallest in the world, and that in turn requires a lower voltage to create the spark. There’s also a laser-welded wafer tip, which is claimed to boost the flame’s ‘kernel’. And this, believe it or not, actually increases the compression ratio, because the spark is bigger, and occurs more quickly (at less than 0.0004 seconds) than with a conventional spark plug. Denso also claims that iridium plugs use less fuel and offer cleaner emissions since more of that fuel is burned. Told you they were clever...
Marko Wowczyna, general manager of Denso here in the UK, argues that iridium represents the current cutting edge of spark-plug technology, combining increased power with both cleaner exhaust emissions and greater fuel economy. ‘Our Iridium Power plug is aimed more at high-performance engines, while Iridium Tough, with its longer life, is more suitable for engines where the plugs are hard to get at. We find our iridium range is selling by word of mouth, and customers seem to accept that while they aren’t the cheapest, they are the best,’ he says.
The latest introduction to the iridium plug market comes from Champion. Unveiled last September, Champion’s plugs also feature a Fired-In Suppressor System (FISS) resistor. Like Denso’s plug, there’s also a lower firing voltage, which keeps the spark active for longer periods than conventional plugs – and creates less strain on the car’s ignition system.
In addition, the iridium technology used is unique to Champion. It lacks Denso’s 360-degree welded tip, and uses an iridium tip embedded with a base nickel alloy around the tip.
Champion says that while its iridium range is a performance offering, it works just as well as a straightforward original-equipment replacement.
What’s more, Champion is claiming longer life from its new plugs, because the iridium centre electrode, along with a platinum pad, uses superior materials. The electrode reaches its temperature more rapidly, and maintains that temperature more efficiently than other plug designs.
A Champion plug’s tip size isn’t as small as that of other iridium plugs: NGK’s is 0.6mm, Denso’s is 0.4mm, while others are 0.7mm. ‘Going to 0.7mm offers a nice compromise between size, durability and performance. Smaller tips can be especially fragile – the iridium material is very brittle, and can crack if handled incorrectly. Larger tips use more iridium than really needed, and start to erode ignitability,’ a Champion spokesman says.
But let’s not forget NGK, the biggest-selling plug brand here in the UK.
Tim Howes, from the company’s technical department, explains the value of using iridium. ‘The material has a much higher melting point and oxidation rate than nickel alloy, and even after this significant reduction in surface area available for erosion the service life can be enhanced by a factor of up to five times.
‘Reducing the amount of material around the firing point produces a faster flame-kernel growth, and a reduction of the transfer of heat energy away from the flame – back into the electrode – which is detrimental to fast, complete combustion. Fine-wire centre and taper-cut ground electrodes provide this for us. Smaller electrodes also mean that less energy is required to initiate the spark – a lower voltage, in other words – which is another benefit,’ he says.
But do iridium plugs offer a longer life and greater performance? The answer’s an emphatic ‘Yes’ from Howes, as he explains. ‘We have had significant feedback from people who have tried iridium plugs. The acid-test is that if they didn’t provide a benefit then vehicle manufacturers wouldn’t specify them, because they could achieve a significant cost reduction by using standard nickel-alloy or platinum types.’
Denso’s Marko Wowczyna says that in the near future iridium plugs are likely to have smaller diameters and a longer reach, a result of engines becoming physically smaller over recent years.
Rob Helmsley, who runs www.spark-plugs.co.uk, says iridium is at the leading edge of today’s spark-plug technology. ‘It’s certainly the best for road cars, and is slowly being adopted here in the UK. While Champion, Denso and NGK offer iridium plugs, Denso is pushing their offering more,’ he says.
Current iridium plug prices are higher than those for platinum – recently platinum plug prices have been in freefall, making them, in some instances, ‘as cheap as chips,’ says Helmsley. Current Ford Zetec direct-replacement plugs cost around £4 plus VAT, whereas a Denso iridium replacement is £7.67 – but prices are constantly falling as more sellers enter the market. ‘I don’t know who’s driving prices down, but we need to sell a lot more as prices fall, and inevitably service will suffer,’ Helmsley suggests.
OTHER TECHNOLOGY
But while iridium is the latest technical revolution to hit spark plugs, one high-performance plug has been around for a good few years – Splitfire. This US-made plug made its mark with American car applications, but lately has been adopted by many Japanese tuners.
‘It really was the first performance plug on the scene, and was available in Split-V and Triple Platinum forms. Splitfire plugs aim to improve the burn through the size and efficiency of the spark, which is why there’s a V-shaped notch in the top of the electrode,’ says Martyn Pearson of UK Splitfire distributor, Triple P. ‘That allows the flame kernel to pass unimpeded into the cylinder in order to reduce misfires, and that in turn offers better power and fuel consumption,’ Pearson argues.
Meanwhile the Triple Platinum does away with the Split-V, and uses three platinum electrodes, which naturally offer a much-improved spark. ‘These have all the advantages of the Split V, but have increased longevity – they come with a 100,000-mile warranty, and have always proved popular with hot-hatchback owners. There’s a loyal following for them,’ Pearson points out. Interestingly, there are no plans for an iridium Splitfire plug.
LOOKING AHEAD
Iridium might well be at the cutting edge of today’s spark plugs, but that certainly doesn’t spell the end for other technologies. ‘Iridium and precious metal are also not the only answer, or way to progress. We have a new, patented, original-equipment-approved, high-durability, non-precious-metal electrode alloy. We are also advancing ceramic technology – for example, our innovative patented ribbed-core nose design fitted as original equipment to most current Peugeot, Citroën and Fiat models – including the new C4. Another development is our Integrated Combustion Sensors in both glowplugs and spark plugs,’ Champion says.
And just around the corner we can expect to see increasingly fine electrodes, for better combustion. According to NGK’s Tim Howes, ‘The ground electrode will also become a fine-wire type, so that the two electrodes will present two needle-like structures in the combustion chamber. This again will provide a less hindered growth of the flame front.’ That means more power, reduced emissions and increased fuel economy.
