What spark plugs to use?

There are quite a number of performance spark plugs in the market that seek to improve performance by its ability to generate unique and stronger sparks. Every spark plugs manufacturers seemed to have their own explaination of their product superiority against other brands. It was really hard to differentiate. To ensure that I made the right choice, I decided to do some research to understand the basic functions of spark plugs.

Interestingly after much research, I've learned that spark plugs doesn't just ignite the air/fuel mixture, it also functions as a heat remover. Yes I said it right, spark plugs have dual function. It works as a heat exchanger by extracting heat generated from the combustion chamber and transfer it to the engine cooling system.

Though its function is to remove heat, it has to retain sufficient heat to prevent fouling. It requires minimum 500 degrees C to perform self cleaning, to discharge carbon deposit at the tip. The picture on the right are examples of dry and wet fouling.

If you push your engine often and frequently touches the redline at 6,000RPM, your engine will be working at high temperature most of the time. This may result overheating at the insulator tip. The plug on the left shows the glazed appearance that is resulted from deposits accumulated on the insulator tip melted at high temperature.

To ensure that the spark plugs function optimally, the temperature at the end of the plug's firing end must be kept low enough to prevent pre-ignition and high enough to prevent fouling, therefore selecting the right heat range plug is very important. There are some who advise owners to install higher heat range (cold plugs), to gain better performance at high speed.

Using a higher than recommended heat range, may result more incidents of fouling that forms carbon deposit that may impedes ignitability. It is recommended to use the correct heat range, unless you run at high speed most of the time, example racing. Since I don't race, I decided to stick with the recommended heat range.

Another popular trend is regap to smaller spark gap. Though it may improve performance by its bigger spark generated, it shortens the life of the plugs. Furthermore it may generate unnecessary combustion heat, therefore reduces compression ratio. Generally the higher the incoming air and engine temperature the lower the compression ratio becomes. Lower compression ratio will compromise fuel efficiency. An0ther disadvantage of setting smaller spark gap is that it lowers ignitability limits, (as illustrated on the left) as it requires richer air/fuel mixture to achieve combustion. Using larger gap allows leaner fuel combustion.

Vios uses Toyota's 1NZ-FE engines. I did a search on all Toyota models that uses 1NZ-FE engines around the world such as Echo, Vitz and Yaris, and noticed similarities in spark gap settings. Countries that are located at Northern & Southern Hemispheres use 0.8mm gap. However tropical countries like Malaysia and Indonesia use 1.1mm gap setting.

Generally in my opinion, as a normal road user I only require transportation that gets me to my desired destination safely and economically. Just to get addition 1% in horsepower doesn't really excite me, especially if I have to compromise fuel efficiency and higher maintenance cost. Of course I will happily welcome any idea that can help improves my car's performance, but the benefits must favour towards fuel efficiency and lower maintenance cost rather than higher performance.

In conclusion, I will choose spark plugs that operates at the right heat range (hot plugs) and at 1.1mm gap setting.

Now that I know what to look for in a spark plug, the next step is to decide which brand would best match my driving style and low maintenance cost.

I shall post my decision in my next posting....