At about 1800 degrees you will start to get NOx, I haven't put a thermistor on mine so I don't know if they get that hot. I know snowmobile 2 cycles push 1400 and they run at less rpm and is liquid cooled. NOx are nitrogen oxides created in combustion. They are associated with the acid rain issue as the rise into the atmosphere and mix with water vapor it creates an acid condition. Below 1800, the nitrogen gets pushed through as N2 as there isn't enough heat to force the NOx bonds.