Spark Plugs

Bang Bang Bang Bang.. thats all a spark plug does, all day long. Pretty simple concept really.. feed it some volts at the right time and a spark jumps across the electrodes, if done in time with the engine this will cause a combustion in the chamber and you have a power producing explosion.

Well Unforntunately things aren't all that they seem in the land of Spark Plugs. You see our 300's (Twin Turbos in particular) run at extremely high combustion temps. Much higher combustion temps, and much greater power producing explosions than anything found in ordinary engines. Also the engines do not like our 96 Octane fuel (or 98 if you go to challenge / Gull). Transient Detonation - very mild non harmful detonation - is quite common. For stock engines that will never get molested stick to the recommended NGK PFR6B-11's.. these are fine. But if, like most, you want to add so more go-go-goodies to your car then the resulting increase in power will increase combustion temperatures. This has a flow on effect to an increased chance of major (harmful) detonation, and also "eating" spark plugs.

How do we combat this? By replacing the standard plugs with "colder" plugs. What does a colder plug do? How does it work? Read these wise words from our resident Z Doctor Ricky:

The higher numbers are colder plugs. A colder plug simply has a better ability to cool itself. When combustion chambers become more violent (higher temps) due to aftermarket toys, the plug sees higher temperatures approaching its critical temperature (~900 degrees C). To avoid plug failure (burning away ground / center electrodes, or just increasing the plug's gap) some people must go to a colder plug.

The reason we cannot use a colder plug from the outset is fear of never getting the plug warm enough. A spark plug must reach what is called its "self-cleaning temperature" (or region) which generally occurs at about 500 degrees C depending on the A/F ratio. This is normally reached during high engine or vehicle speeds. This "self-cleaning temperature" allows the plug to burn off carbon deposits accumulated at lower speed and idle conditions. If this temperature is not consistently reached, you will have definite fouling problems.

So why did I mention PFR6B-11B's as opposed to something like a PFR7B-11? Well the 6B-11b's were a special design plug that Nissan commisioned NGK to produce. As per the picture below, the 11B is the plug on the right, you will notice it has a longer shroud, this brings the plug's electrode further into the cylinder to move the "fire" away from the cylinder head - As carbon+heat buildup in the cylinder head was a recognised contributer to Detonation.

So what plugs do you buy?

For standard Twin Turbos NGK PFR6B-11 (left)

For modified Twin Turbos NGK PFR6B-11B (right)

Written By Rowan Hick, member #001, rowan@600plus.com