Rear Fibreglass Diffuser

Had an old mirror I picked up via freecycle locally. Makes a great platform to lay fibreglass.

3 layers with minimum resin.

Once set, it peels off easily and give a really good surface underneath.

Lay up a smaller sheet with black dye to the resin.

Mark out and cut some tapered sections.

Lay the large sheet, cut some slits and position the vertical black `fins`.

Yeah, that`s right, I`m making ANOTHER diffuser…

The outer sections are stepped down to clear the exhaust. It kept rubbing on the old aluminium one.

Cut more slots and fit the fins through the slots. Extend above the `top` of the diffuser to allow a strong joint between the pieces.

The outer sections are lower, which reduced the diffuser angle. To compensate and keep the area increasing, the outer vanes are radiused outwards.

I seem not to have any photos showing the securing method. It`s all fibregalssed from the top, so no intrustion into the airflow. Easily removed with no access required under the car, just remove some nuts from behind the rear bomper and it all slides off. I WILL take some photos.

Painted and fitted.

Some shots showing it from Cadwell yesterday.



I`ve been told that it produces rather a lot of spray….

Lighter than the old aluminium one, extends MUCH further under the car. Covers the void under the car and fastens to the floor where your feet would normally go if you were sat in the back.

Have a quick look around the car today. No issues to report

The water left some nice trails on the diffuser

The diffuser needed to be removed to do some other stuff anyway, you can see the air flow being sucked towards the centre. There is obviously a lot of turbulence being picked up from the wheel. No real way to avoid this. That`s what the rubber `skirt` was for on V2, I may look at adding a small one to the side of the diffuser around the wheel area.

The outer section, nearer the wheel has more turbulence

As promised, these are the securing arms in the middle of the diffuser

They slot into these sections of box

I also looked at the Evolution of the Diffusers I`ve made.

Version #1

Version #2

Version #3