Some of you might remember I attempted an undertray once. I lost confidence because of fluid leaks that I thought would collect on it. Then I also lost confidence in my attachment methods. I still have an oil leak (last one I believe). But I really wanted to finish my rear diffuser at least. Here it is.
Calculations aerohead taught me suggested that I needed a 4 degree angle on the diffuser.
I was not able to accomplish that. This is about 5 degrees, which is going to have to be close enough for now.
Also, I know the diffuser is less effective without a full bellypan. But I do have a low airdam and low side skirts. The remaining airflow under the car, I am hoping will benefit from not hitting the rear bumper cover parachute just before separation.
Here is what it looked like underneath (muffler is missing):
Here is what it looks like now (I used the same black plastic sheet that the wheel well skirts and grillblocks are made from):
I deliberately left a modest overhang in imitation of some features of cars I see rolling about. I am okay with it, but I will probably trim it more:
The overhang also made it possible to achieve solid attachment without drilling any new holes in the car's frame or bumper cover.
I plan eventually to cover parts of the middle section that are especially bad, but not right now. Too much else to do. Gotta get the car ready for smog check and for school dropoff runs.
EDIT: For reference here is the cardboard template I made for the diffuser:
