Diffuser

From Nissan 350Z & 370Z Wiki

A diffuser is an aerodynamic device which equalizes the pressure and velocity of air traveling underneath a vehicle to the level of the air surrounding the vehicle.

As air is driven underneath a moving vehicle it tends to be accelerated and begins to lose pressure. This process aids in creating downforce by generating a slight vacuum below the car. As the high velocity air exits from the underside of the vehicle it collides with the slower moving atmospheric air and turbulence is created. This bubble of turbulence creates drag, which hurts aerodynamic performance.

The diffuser provides an area for the air to expand, which slows it’s velocity and brings it’s pressure more in line with the surrounding air. Thusly, smoothing it’s transition as it exits the underside of the car.

The 350Z is fitted with underbody diffusers on certain models (Track, Grand Touring, and 35th Anniversary Edition). On the 350Z the diffusers are used, along with the front chin spoiler, to create a Zero-Lift condition. Basically the 350Z does not generate an appreciable level of downforce. Instead the aerodynamic package prevents the car’s silhouette from acting as a lifting body. The practical upshot of this configuration is a measure of high speed stability without the drag inducing penalty of large downforce generating wings.

The stock underbody diffusers can be added to any model of 350Z not originally equipped with them from the factory. They are available from the parts counter of you local Nissan dealership or through many online retailers