Do I Need To Use A Resistor Plug?
Today's spark plugs use resistors to eliminate radio frequency interference (RFI) which can affect on-board computer or ignition systems, AM and FM radio reception, and TV broadcasts. Each time the spark jumps across a gap, an electromagnetic field is created that can interfere with radio signals. By placing a resistor in the spark plug, we can substantially reduce RFI. Furthermore, the use of non-resistor plugs with today's complex computer systems can result in driveability problems, loss of performance and can even cause the computer to store trouble codes.
Many motorcycles produced now have computer controlled ignition and/or fuel injection systems. RFI can effect these components. Several motorcycle aftermarket ignition modules are sensitive to RFI. Most notable among these are some modules produced by DynaTech. Use of proper spark plugs and ignition wires will eliminate the problems observed.
How Does Heat Range Affect A Plug?
As discussed, a spark plug is made up of ceramics, steels and nickel alloys. These materials do not have the ability to produce energy or heat. When we talk about the heat range of a spark plug, we're referring to its ability to move heat away from its tip or core nose into the cooling system. A cold spark plug would have a cooler tip temperature than a hot one. With today's fuels, we know that anytime the tip of the ceramic core nose goes below 850 F, carbon will build up and the spark plug will foul. We also know that if the tip temperature of the plug exceeds 1550', the metals will begin to break down. At approximately 1700, the plug will glow and can become a source of pre-ignition within the combustion chamber. Armed with this information, it becomes clear that maximum performance can be achieved with a spark plug that has a temperature of greater than 850 at idle, but no more than 1550' under wide open throttle.