1.Put the car on flat ground, in park, or first gear with the ebrake engaged. Jack up the rear of the car with a floor jack or bottle jack using the rear jack points. Place jack stands or cribbing under the control arm. Remove the rear tires. It is good practice to place the tires under the pinch seam of the car as a safety measure if a jack stand moves or fails. 

2. Remove the three T25 torx screws that hold the back of the wheel liners to the bumper. Two inside the wheel well, and one going up into the bumper from below. Repeat on the other side. 

3. Pull the liner forward. Looking into the bumper cavity you can see the two T25 screws that hold the plastic bracket to the edges of the valence. Remove both on each side. 

4. Take note of how the bumper lip and valence lip are sandwiched inside this clip. We will need to reinstall it in the same way. 

Pull the outer edge of the clip towards the center of the car. Once the outer edge releases, slide the second half of the clip forward. 

5. Open the diffuser box. Remove the packaging. With the machined pockets of the baseplate facing up, slide thefins onto the baseplate until they lock into place. The fin hole should be on the top. Only install the inner two fins (larger ones) at this step. 

6. If you are having a hard time getting the fins to click in, hold the baseplate against your chest, then grip the fin with your hands and pull it towards you to press it into place. The brass threads on the baseplate should line up with the hole in the fin. The fins have some adjustability forward and back to line them up with the retaining screw. 

7. Install the black M4 bolts using a Phillips head screwdriver. You can use thread-locker on these screws, however it is not necessary. They just need to be snug, do not over tighten. Fasteners this small can be easily stripped. 

8. Locate the M6 bolts, and nylock nuts in the hardware bag. Grab your clamps, a 4mm Allen key, 10mm wrench and a drill with the 6mm or ¼” drill bit. 

The next steps are shown on a workbench for better lighting. You do not need to remove the valence from the car. 

9. Hold the baseplate and fin assembly tight to the valence with the countersunk holes facing down. Place a clamp on each edge to keep it in place. Now adjust it left or right to center it. Check the outside edges, and notch in the center to make sure that your gaps are consistent all the way around. 

10. Wear safety glasses and drill the two center holes with a 6mm or ¼” bit using the baseplate as a guide. Install two bolts, and nylock nuts. Hold a wrench on top, and turn the bolt with the allen key. 

11. Now drill the remaining holes in the baseplate, and install the hardware. Now you can install the outer two fins, and secure them with a black fin screw. 

12. The spats are left / right side specific. The countersunk holes will be on the bottom. The narrow end of the spat should be closest to the wheel well. 

13. Have a clamp ready, or second set of hands to help hold it in place. Hold the spat up to the edge of the valence/bumper. There is about 6mm of adjustment available to slide the spat left or right to align it. The edge near the wheel well should be flush with valence. The edge closest to the exhaust should be tight to the back raised lip of the valence. 

14. Once you have the position set, drill the hole closest to the wheel well. Drill slowly. There is only a small distance between the bottom and top of the valence so you need to control the drill once it goes through the valence. Install the smaller bolt (M5), and nut. Install it snug, but with enough room to rotate the spat if needed. 

15.  Check that spat is still in the correct position, now drill the next hole, working towards the exhaust. Install the shorter bolt & nut. Fully tighten the first two bolts.

16. Lastly, drill the hole closest to the exhaust. This hole will land on an angled portion of the valence. Install the last bolt and nut. Just snug this bolt, so you do not deform the valence plastic.  This last hole should be an M6, and you will use the two longest bolts in the bag. 

17. Reinstall the valence clips onto each side. Reinstall the clip screws. Line up the fender liners, and reinstall the three screws on each side. 

Reinstall the rear tires. Once the car is back on the ground, torque the lug nuts.