Spark Plugs

Denso Iridium

Iridium outboard motor spark plugs

Iridium spark plugs are the biggest step forward in sparkplugs in many years.

Why choose Iridium over a regular spark plug?

Relatively recent advances in fabrication techniques have enabled the use of Iridium – an incredibly hard precious metal, for the construction of spark plug electrodes. Laser welding technology is used to weld the Iridium tip to spark plugs manufactured by Denso. It’s worth noting that spark plugs can’t increase the potential power that an engine can generate but a more efficient spark will provide more efficient combustion and associated performance and economy benefits. A poor spark from a worn or low grade spark plug will reduce efficiency. An Iridium plug will produce a more efficient spark.

Notable properties of Iridium are its melting point – approximately 2450 degrees C, considerably higher than Platinum, and it’s strength – approximately 8 times that of platinum. The table image compares the characteristics of Iridium with those of other precious/semi-precious metals commonly used in the construction of spark plugs.

Because of the properties of Iridium, the spark plugs centre electrode can be made with a much smaller diameter than with platinum types (usually 0.8mm for NGK and 0.7mm for Denso), Gold or gold palladium and copper/nickel types. This means that spark plugs potential difference is more concentrated and hence less ‘spark jump’ voltage is required – this can be as much as 5,000 volts less than with standard plug types. Ignition is improved and less strain is placed on the ignition system. Benefits of improved ignition/combustion include better fuel economy, increased power/acceleration and especially better throttle response.

How do Denso Iridium plugs compare to NGK’s?

Construction of NGK and Denso plugs is similar for the most part, the big difference being Denso’s use of a 0.4mm Iridium tipped centre electrode – claimed to be the world’s smallest production centre electrode, where NGK’s is 0.6mm. As with NGK Iridium, and indeed most other spark plugs, the narrower the centre electrode is, the lower the potential difference (voltage) that is required to jump the gap between centre and ground electrodes. It follows that the Denso plug will require an even lower ‘spark jump’ voltage than the NGK plug. The Denso plug also utilises a ‘u-grooved’ ground electrode which is claimed to aid in the production of a ‘flame core’ which further improves the combustion process. In theory, all the benefits offered by the NGK Iridium are further improved by the Denso Iridium with the exception of service life. The smaller diameter of the Denso centre electrode means that less wear can take place before the plugs’ optimum service life is exceeded.