Your car has a computer that has some software loaded on it by nissan before it leaves the factory.
This software decides how much fuel to inject, and when to fire the spark plugs based on how much air it sees going in to the engine.
If you start to increase the amount of air going in to the engine (i.e. by modifying it), the nissan software will not handle this efficiently. It will think there is a problem with the engine, and go into a safe mode - slowing the engine down.
You can install Nistune hardware into your computer, and that allows a tuner to easily change the software on it that tells it how much fuel to inject, and when to fire the sparkplugs - so the engine runs optimally based the greater amount of air now entering the engine.