Points well taken on the ducting, and I'm happy to say I've created a very solid inlet to my oil cooler. It fits flush with the bumper grille, and maintains a few key characteristics.
1. Inlet area smaller than the oil cooler face.
The air rushes in the inlet, then you expand the ducting gradually to the oil cooler so the volume increases. This volume slows the air down, increasing pressure at the face of the cooler. This increases the pressure delta on the face and exit of the cooler, driving air through it. My inlet area is ~33% smaller than the heat exchanger area.
2. Gradual slope.
The maximum recommended expansion rate is 15 degrees, which I set my lower plate to. This keeps the air attached to the walls and prevents it from becoming turbulent.
3. Leaving a gap to the radiator.
Because of my damaged undertray/fender liners, leaving a gap to the radiator reduces the pressure required to force air through the oil cooler. This gives the exiting air an opportunity to be sucked away to a low pressure zone, potentially one below the car. If my radiator area were fully sealed, the oil cooler should be as close to the rad as humanly possible.
4. Completely sealing the ducting.
Using a flashlight, I tested to ensure there were no air gaps between the inlet ducting and the oil cooler face. Aluminum tape is on the way to cover the seams of the inlet ducting itself.
5. Inlet faces the direction of incoming air.
Self explanatory.
I'll be shaking this down at Summit Point this weekend. If temps continue to be higher than acceptable, I'll explore getting a new undertray, fender liners, adding exhaust ducting, and potentially a hood vent. Ideally I'd like to stabilize around 250F.
