Types Of System
There are three basic types of nitrous systems: Dry, Wet and Direct Port.
Dry
Dry nitrous systems are so called because the fuel required to produce the extra power with nitrous is supplied by the car's regular fuel injectors. This means the upper intake is dry of fuel. There are two ways this works: the first is to increase the pressure to the injectors with nitrous pressure from the solenoid assembly. This increases the fuel flow in the same way that turning up the pressure on a garden hose does. The second method is to increase the amount of time that the fuel injector is open and spraying fuel (injector duty cycle). This is done by fooling the ECU and "tricking" it into supplying the extra fuel. In both cases, once the fuel has been added, the nitrous can be introduced and the increase in combustion burns the supplemental fuel to generate the extra power. Due to the limitations of the stock injectors, it is advisable to use jets no higher than around 75bhp.
Wet
Wet systems are named due to the way they inject fuel into the upper intake, normally 3-4" ahead of the throttle body (ie. in the T U R B O charge carrier pipe on a FRST). Wet systems are best used in Turbocharged / Supercharged applications. This is due to the way fuel flows differently than air or nitrous. This difference can lead to distribution problems and sometime inlet backfires. Inlets designed for wet flow (such as carburetors) cause significantly less separation of the nitrous/air and fuel. As the inlets on a modern fuel injected car are designed to flow only air, they have tighter turns and are often of a more compact design - not ideal for wet flow nitrous systems.
Direct Port
Direct Port systems, as the name would suggest, introduce nitrous and fuel direct into each inlet port of the engine. These systems add the two through what is known as a "fogger nozzle". The fogger nozzle meters and mixes the nitrous and fuel supplied to each cylinder. The system works on the same principal as individual throttle bodies - it allows for the precise control of both fuel and nitrous for each individual cylinder for optimum performance. A direct port system contains a distribution block and solenoid assembly with tubes supplying the nitrous and fuel to each fogger nozzle. Direct Port is the most controllable and accuate method of nitrous injection, although installation is fairly complex due to the need to drill and tap the inlet manifold for each nozzle and the plumbing must be routed to clear any obstructions.
i hope this article has answered your question. And in my opinion the better one is which that is suiatble for your application.