The reason why simple Denso spark plugs works better than platinum or irridum in Baleno
Which Spark Plug Composition Should You choose?
The basic spark plug is made of copper, which is actually a pretty good conductor of voltage. The problem with copper is that it is not as hard as some metals and it therefore wears down with the high pressure and heat inside the engine. This wear eventually causes the plugs to foul and work less efficiently over time.
The wear also can cause the air gap in the plug to increase, which can cause a loss in vehicle fuel efficiency and even misfiring in extreme cases. This is because it takes more and more voltage to jump between the electrodes the greater the air gaps widens. One way around this is to use a harder metal, like platinum.
Platinum is a much harder metal than copper and has a much higher melting point. This gives platinum the advantage of lasting longer than conventional coper plugs. Besides longevity, platinum plugs in themselves do not make the spark better, or more efficient than copper in any way.
The main advantage of platinum over copper is its ability to heat better, which subsequently burns off deposits better, and its ability to handle high heat, also enables the plug to hold up better and reduce the amount of air gap change over time.
The only way that a platinum plug could be considered any better at creating fuel efficiency for an engine, is if it can reduce the size of the center electrode to the size of a fine wire tip. This reduces the chance of quenching, because it leaves less area for the heat to be reabsorbed by the plug.
His design also gives the added benefit of needing less voltage to jump the gap in order to create a complete burn. This can be an particularly nice benefit for older engines with less efficient ignition systems. Both benefits give the combustion process the potential to create a more complete burn and therefore greater fuel efficiency.
Iridium is said to be six times harder and eight times stronger than platinum. This means that spark plugs can have even finer electrodes than ever before and still have excellent wear characteristics. Platinum is precious enough, but iridium is even more precious, which is why it is hard to find a single platinum plug for much under $6-$8 and an iridium plug for under $12-$14.
Is it worth the extra cost for platinum and iridium? Yes and no.
If you are willing to change your plugs once every year or two depending on your driving habits (and it is actually quite easy to change your spark plugs), copper plugs can offer good performance and efficiency. It is also worth mentioning, that with platinum and iridium plugs you generally get what you pay for.
The more expensive the plug, the more platinum (double/triple coated) or iridium is usually used in the plug. A thin coating of these precious metals will not fair as well as a thicker, so in general, you won't want to go the cheap route, as it would be better to just use good old copper for your maximum value.
However, in general, the standard copper plug does not reduce quenching like many of the platinum and iridium plugs can. With this said, technology has opened copper type plugs to the similar benefits of the fine electrode using various configurations and shapes. This is where the specialty plug comes in, such as the U-groove or Splitfire.