NGK IR (Iridium) Spark Plugs for Motorcycles


Most of us have heard about NGK IR (Iridium) spark plugs. These are plugs commonly used in the hope of maximizing performance and efficiency, but how much can it really change your machines performance? We take a look at the facts and me being an automobile specialist myself, I reveal all about it.
The Basics: The primary function of the spark plug is to ignite the air/fuel mixture within the combustion chamber at all RPM’s. Spark plugs must provide a path for the flow of electrical energy from the ignition coil to create a spark used to ignite the air-fuel mixture. Sufficient amount of voltage must be supplied by the ignition system in order to create a spark across the spark plug gap. This is called the ‘Electrical Performance’. All the conventional plugs fail to supply proper voltage when its tip gets carbonized or when the resistance of the plug becomes too high. The resistance power basically depends on many factors. Many people install IR without any high performance plug cables, this can create resistance in the wires when it comes to long term use.
Why? IR is basically connected to an ignition coil through a cable. For IR the best cable is high performance cable and so too is the required coil. The ignition voltage in the combustion chamber is nearly about 18000V. These days’ high performance coils can be found on various bikes, For example a Royal Enfield has coil which gives about 24000V, MSD ignition gives about 44000V. That’s a lot of voltage to be dealing with and in order for it to reach the plug without much loss, the need for high performance cables arises.
A spark plug firing end temperature must be kept low enough to prevent pre-ignition, but high enough to prevent fouling. This is called “Thermal Performance”, and is determined by the heat range.
Plug Replacement Time: Unfortunately, there is no fixed answer to this. As spark plugs grow older, they lose their sharp edges as material from the centre and ground electrodes are slowly eroded away. As the gap between these two points grows, the voltage required to bridge the gap increases proportionately. Even the best ignition systems will be strained to supply enough voltage to completely burn the fuel. It is at this point, that the spark plug would need a replacement.
Replacing worn out spark plugs with new ones (with sharp new edges) effectively restores the ignition system’s efficiency. Misfires are reduced, power is restored, economy of operation is enhanced and emissions are reduced.
Cleaning of IR: Yes, you can clean spark plugs. However, it is good to remember that spark plugs are a vital component, so it’s important to make sure you check to see if it’s worth cleaning before you go through the following steps.
  • If the firing end is wet, make sure you clean the spark plug with a quick drying cleaner. (Examples: contact cleaner or brake cleaner).
  • Sand blast the spark plug using low air pressure and use a dry compound.
  • Completely blow all the sand from the spark plug.
  • Using a wire brush clean the threads and re-gap.
NOTE: Insufficient cleaning of the spark plug may lead to spark plug failure in a very short period of time. Clean the spark plug thoroughly to avoid problems later. Remember, if a spark plug is fouling it’s usually a result of engine side factors or incorrect heat range selection.
Performance gain after installing the plug: A common misconception is that changing spark plugs will result in a large power increase. In most cases, removing even seriously worn out spark plugs will only result in tiny power gains, typically about 1-2% of total engine output. This could be even less for computer-controlled vehicles, primarily because most newer vehicles have more powerful ignition systems and the vehicle’s computer can make adjustments so that vehicle operation is not affected by the resistance generated by the spark plug.
Many people think that simply supplying more spark to the firing tip can and will combust more fuel. What they don’t understand is that most new fuel injected vehicles are designed in a way that they can use even the last drop of fuel. So fitting a better spark plug wont be able to make any sort of changes here as the computer already controls the fuel pump and injector along with the sparkplugs.
When a stock or near-stock engine is given a fresh set of spark plugs, peak efficiency is restored. The power gains that come from this restored state of tune are usually minimal. Any company that tells you that their spark plug will provide significant gains in power in a stock or near-stock engine is making blank statements that may not be supportable.
List of Iridium plugs:
  • NGK IR
  • Denso
  • OWS
  • HKS
  • Autolite Plugs
  • Bosch
  • TRD
  • UMI
  • Volkar
  • MOBO
  • RalliArt
  • Brisk
After Looking at these manufacturers of Iridium don’t ask me which one is the best. Because so far I have used an NGK IR plug. One advice I would like to give IR users is to use a cleaning machine for the plug instead of any emery paper or sharp tool. Always try not to damage the tip of the plug.


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