Not normal diffusers. I want to know how exhaust inject diffusers work. Thanks.

Not normal diffusers. I want to know how exhaust inject diffusers work. Thanks.

I am not familiar with that term, can you elaborate?

Injecting the exhaust into the rear diffuser can also help extract the air from below the car. The exhaust gasses effectively energize the boundary layer, helping to raise the pressure of the low-pressure, fast-moving airstream back to the ambient atmospheric pressure at the exit of the diffuser. This helps extract the air more efficiently from the underbody.


taken from wikipedia. Im a little confused how that works. I get how they use exhaust to extract air, but how?

Not up on that, must be the hot air.

I am a mechanical engineer and that still seems faulty in its logic. The last part of the sentence is what I am talking about. The boundary layer as far as fluid are concerned is the area next to the surface(in this case either the exhaust piping inside lining) is where the air is actually not moving or moving in a very different way. The most common diffuser is HVAC diffusers or grilles in the celing. They distribute air out of an orfice. The exhaust does the same thing but having the quad pipes cut off and seperate from the main exhaust piping is quite odd. I don't see the engineering in that.

BTW, wikipedia is done by the general public so it is possible this wasn't written up correctly.

It helps to get the air under the car flow faster, this in turn will cause a negative pressure that will actually create down force. This is why we donr see the huge wings on cars like we did in the 80's and 90's

A diffuser would be pretty useless without a complete undertray to keep the air flow laminar under the car. Putting exhausts in this region of low pressure as air is expanded out the rear of the car might provide some exhaust extraction, but these advantages would be academic at any legal speed in the US.

A diffuser would be pretty useless without a complete undertray to keep the air flow laminar under the car. Putting exhausts in this region of low pressure as air is expanded out the rear of the car might provide some exhaust extraction, but these advantages would be academic at any legal speed in the US.


I don't think legal speeds or exhaust extraction is a consideration

We live in an era of factory rice and many cars today now have fake looking diffusers or basically non-functional diffusers on their rears. It looks cool but unless you are going 150mph, well.....sigh....