installation instructions

rear diffuser

installation notes

**For installation on non-GT4 981 Caymans and Boxsters, the flat undertray section typically uses 2 fewer mounting points due to the difference in the rear subframe (2 less rivet nuts). On some of the 2014 model years these mounting points for rivet nuts are missing and it requires drilling to secure mounting holes for the undertray.**

required tools & hardware

***DBJ is not responsible for damage to you or your vehicle by installing our products. Avoid improper installations that can lead to damage by using a professional for all installations.***

TOOLS REQUIRED                                                  INCLUDED HARDWARE

4mm Allen                                                            66x    M6X15 Screws

10mm  Socket                                                        2x      M6X30 Screws

16mm Socket                                                            2x      M6X80 Screws

T25 Torx                                                                    62x    M6 Washers

             T30 Torx                                                          4x      M6X35 Hex Flange Screws

14mm wrench (socketing best)                                  4x      M6 Stainless Steel Rivet Nuts

Socket wrench                                                           6x      M6 Nuts

Extensions                                                                  4x      M8 Nuts

Pliers                                                                    2x      M6 Clip Nuts

            Flat Head Screwdriver                              2x      51mm Unthreaded Aluminum Standoff


Drill with a 3/8" drill bit                                                                                                      

assemble the strakes

Assemble the 6 strakes with their mounting brackets using a 4mm allen and (4) M6x15 screws per strake. Notice that the mounting brackets are L shaped with one leg longer than the other. The blue arrow is pointing to the shorter leg of the mounting bracket and the green arrow to the longer leg. The shorter leg is the side that should mate to the strake as shown in the middle picture above. The red arrow is pointing to the install direction of the M6x15 screws. On the right picture you can see that there are two ways to install the mounting bracket onto each strake. You will need to assemble (3) in the "left configuration and (3) in the right configuration so that they will match up with the diffuser hole pattern.

attach strakes

Insert the strakes into each slot as shown in the picture on the bottom left. Make sure mount on the strake is lined up with the holes in the diffuser. Right mounted strakes with holes to the right. We assembled (3) right ones and (3) left ones in the previous step. Once the strake is inserted, push the strake out towards the rear(of the car). You can then slide the strake to the front (of the car) and line up the slot in the diffuser with the hook in the strake as shown in the bottom middle picture. Next pull the strake towards the front as much as possible to reduce the gap between the diffuser while securing the strake with (4) M6x15 screws and (4) M6 washers from below as shown in the pictures to the bottom right and right. You will need to use the 4mm allen to secure these screws. Repeat until all the strakes are attached to the diffuser.

attach flat underbody tray

Align the flat underbody tray slots with the slots on the diffuser as seen in the bottom left photo. We like to shift the slots back about 1/8" so that the rear diffuser will stick out a little further back as a starting point. Please note that both the diffuser and the flat underbody tray have tabs that fold up(green arrows). Don't install the flat underbody tray upside down! Use (6) M6x15 screws, (6) M6 nuts, and (12) M6 washers as shown in the bottom center picture. Use one washer on the screw side and one below the M6 nut to sandwich the diffuser. You will need to use an 10mm socket and a 4mm allen. 

install m6 rivet nuts

This section can be the most difficult part of the installation due to the high torque required. Let's begin by opening holes in the subframe by using a 3/8" bit and drilling the existing holes as seen in the top middle picture. There are (4) holes that need to be opened up for the GT4. For regular Cayman, Cayman S, Boxster, and Boxster S models, only the (2) inner holes need to be opened and rivet nuts installed. On some model years (2014) this feature is missing. To install the flat underbody tray on these models, a custom hole will need to be drilled into the tray and subframe to attach the tray securely to the car. Please use a rivet nut tool if available or use the hardware supplied. You will need (4) M6x35 hex screws, (2-4) M6 washers, and (2-4) M8 nuts. Put the steel rivet nut, washer, nut, nut, and screw together as shown in the top left picture. A 14mm wrench and 10mm socket will be required to install the rivet nut. The 10mm will be used as shown in the top right photo. Place the rivet nut flush into each drilled hole and torque the screw clockwise while holding the nut still with the wrench. Repeat this 4 times for each hole. It is highly recommended to use extensions and long lever arms to get enough torque to install the rivet nuts. The rivet nut should be fixed and not slip out or twist when installed. **After each rivet nut is installed, please discard the M6 hex screw. 4 are supplied because they deform after each rivet nut is installed. Be careful as some may even shear if you torque the screw too hard.

lower subframe brace and install main bracket

Using a 16mm socket, remove the front (2) nuts on the rear of the subframe brace (red circles) as shown in the bottom left picture. The (6) blue arrows are pointing to other nuts that will also need to be loosened. Lower the subframe brace just enough to slide the main bracket in as shown in the bottom middle picture. This may require the use of a pry bar. The bracket should fit flush against the brace as shown in the bottom right picture. Once you ensure that the bracket is installed centered to the subframe brace, reinstall the (2) rear nuts and tighten all (8) of the subframe brace nuts with the 16mm socket. Torque the nuts to 65ftlbs.

Install rear mounting brackets

Next to the rear exhaust muffler tips, (2) rear mounting brackets must be installed as shown in the bottom left photo. Note that the final installed position has a slight angle slope down towards the muffler (very slight V). Using a T30 Torx remove the two screws. One of these screws is highlighted in the bottom middle picture. There is a slot at the top of the bracket for the original screw to be reused. Try to align this bracket in the center of the slot and tighten. Adjustments can be made if necessary later. Finally the rear of your car now should look like the bottom right photo with the blue arrow pointing to the main bracket and the red ones pointing to the installed rear mounting brackets.

install m6 clip nuts

Remove the (2) OEM Torx screws using a T25 Torx. Then remove the (2) OEM rear clip nuts in these locations(circled in red) in the bottom left picture. You will need to use a set of pliers and maybe a flat head screwdriver. Insert in these places the supplied (2) M6 clip nuts as shown in the bottom middle and right pictures. Please make sure that the clip nut is centered as shown in the bottom right picture so it will be easier to install the long M6x80 screw.

Install the diffuser

Finally it's time to install the diffuser onto the car! The green circles are M6x15 screws and the red circles are the M6x30 screws (These red circled screws will not be used in the installation of the regular Cayman, Cayman S, Boxster, and Boxster S models). Be sure to use an M6 washer for each of the M6 screws that are used to hold the diffuser to the car. It is easiest to start by installing one screw near the front of the car and one at the rear main bracket. Install the screws by hand and do not tighten them fully yet. Try to mate the front of the flat undertray tab as flush as possible on the rear subframe near the oil pan as seen in the bottom left photo. Next install the purple screws.These are long (2) M6x80 with (4) M6 washers each and (1) 51mm standoff as shown in the bottom middle picture. Stack the washers as such where one is used underneath the diffuser and the other (3) directly on top. The standoff will sit onto of the (3) washers all should be the only part touching the M6 clip nut/bumper that was installed in the previous step. Once all the screws have been installed by hand, you can shift the diffuser slightly in all directions. Try to line up the holes the best you can and make sure that the diffuser is not touching your bumper. Lastly tighten all the mounting screws down when the diffuser is in place and enjoy!