Before you can choose the right glow plug it is essential that you understand how the glow plug works and effect the performance of your motor.
The glow plug element is made from several metals alloyed together, including platinum. After the motor has been started, using a glow clip, the plug continues to glow as a result of a catalytic reaction between the platinum in the plug element and the methanol in the fuel. This catalytic reaction causes the plug element to glow and, as the fuel is compressed by the piston, the glowing element ignites the fuel.
For your engine to be running at its optimum level the fuel should egnite when the piston is at top dead centre (TDC), driving it back down and up for another stroke.
When nitro is added to fuel it advances the fuels ignition point (makes the fuel easier to ignite) and so a glow plug which caused fuel with no nitro in it to combust at TDC will cause fuel with nitro in it to ignite before TDC reducing the performance of the engine.
In order to prevent the fuel from igniting before TDC it will be necessary to use a glow plug with a cooler glowing element. This is why glow plugs are referred to as HOT, COLD or anywhere in between.
The point to realise therfore is:
The lower the nitro content, the hotter the glow plug should be.
Or, conversely:
The higher the nitro content, the cooler the glow plug should be.
