I've been thinking about integrating a rear diffuser from a newer car. One of the obvious reasons for this is that the area below the bumper in my car is totally f#%ked up. Its got huge dents and bents and as a finishing touch, somebody has totally rape the area of the original exhaust tail pipe location with a hacksaw!
An old picture where all this is visible:
I wanted something subtle with dual exhaust and after several hours of searching on the internet and constantly looking at rear diffusers on parking lots etc. I finally decided to go with an Audi A4 B6 unit. The curvature of the part is definitely not the perfect match off the shelf since the rear of the 240Z has only a slight curvature, but after some minor modification, the fitment was surprisingly good. The OEM Audi part is a made of plastic and this is a key point to notice. There are good looking carbon fiber tuning parts for Audi, but they simply wont fit the 240Z. The plastic part can be forced to follow the shape of the 240Z rear.
This is the diffuser I used:
In the Audi, this part is attached to a plastic bumper. The orignal retaining scheme needed to be modified. Also some reinforcement plastic needed to be removed so the part will bend more easy.
I made these rectangular shaped cuts to the rear valance where the diffuser is to be attached. The diffuser is fixed in place with metal clips from the back side (I forgot to take a picture of those clips).
The fitment is already quite good although I did not fix the part with the retaining clips yet in these next photos. I still need to fabricate some sheet metal to the sides. There is also a screw hole on the side of the diffuser so I need to make a bracket for that inside rear quarter panel. I plan to weld a small-diameter metal bar along the top seam of the diffuser to create a sort of lip above the diffuser which is going to sit flush with the surface of the diffuser. The metal bar is then bondoed to the sheet metal so that everything integrates together nicely. My new fuel inlet location is also visible in these pictures.