Answer:
it dosent unless you spray too much.
Well due to the greatly increased cylinder pressures created by using NOS, the engine as a whole is placed under greater stress than it would be under normal driving conditions, especially the parts involved with the combustion chamber. A standard engine with components not able to cope with the increased stress imposed by the use of nitrous systems can experience major engine damage, such as cracked or destroyed pistons, connecting rods, or crankshafts.
Even if the engine is up to the task, severe damage can occur if a problem occurs in the fuel system; an engine running with nitrous oxide depends heavily on the proper air to fuel ratio to prevent detonation from occurring.