Reliability As with all modifications to increase power, the use of nitrous oxide carries with it concerns about the reliability and longevity of an engine. Due to the greatly increased cylinder pressures, the engine as a whole is placed under greater stress, especially the parts involved with the combustion chamber. An 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. For example, if the engine's fuel supply were to be reduced, this would cause the engine to run lean by whatever degree the fuel delivery was reduced, which can lead to engine knock or detonation. Depending on the engine, this may only need to occur for a matter of seconds before major damage occurs. It is essential not to reach a fuel cut rev limit as this will also momentarily restrict the fuel flow to the engine and as nitrous is still being injected into the engine without the additional fuel the engine will again run lean and cause detonation. Some mechanism to disable the nitrous system when knock is detected by a knock sensor would be beneficial. Ignition timing must also be watched closely when using nitrous oxide. It is said that for every 50 horsepower of nitrous used, two degrees of timing must be taken out. This is recommended for any stock type application. It is also recommended that high octane fuel (91 octane minimum) be used to avoid detonation. Good optimisation of enrichment fuel is essential otherwise the fuel can 'drop out' and puddle in the intake tract, potentially causing a backfire. With a properly designed nitrous injector and correct placement of the nozzle (not too far from the intake entry point and away from any abrupt bends and restrictions in the intake tract) backfires can be avoided.