APR Performance Rear Diffuser Install w/ JDM Rear Aprons

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This diffuser can be found on APR Performance's website below, and will fit WRX/STI's from 02-07.
APR Performance - Subaru Impreza WRX Rear Diffuser

This diffuser will fit MOST rear aprons/spats, including the 04 and 05 JDM rear apron with little or no additional modification. I am installing the FPR version on my 04 WRX with the 04 JDM rear apron, which is already installed. Although APR does include instructions with the packaging, it never hurts to go into more detail. I also found the photocopied pictures included were very difficult to see.

If anything is confusing or unclear, feel free to PM me, and I will try to explain it better and clarify it in this article.

Tools/Supplies Needed:

Metric Sockets, wrenches, and allen wrenches (hex keys).
Power Drill w/ drill bits
Dremel - optional
Misc hardware explained in the how-to
Tape


The diffuser is in two pieces with three adjustable mounting arms loosely bolted into place. Also included was a set of instructions, some brochures, and a package of hardware.

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The first thing is to remove the rear recovery/tow hook. You will not put this back onto the car. If you wish to keep the recovery hook, you will have to drill a slot for it in the diffuser. I will be removing mine.

Three bolts hold it on. Two that mount straight up to the frame, and one more on the side. Although both ends are in a bolt shape pattern, only ONE is actually removable! The other is welded on. Don't do what I did and accidentally snap it off (on a previous mod). If you do, don't worry, it's not going back on the car. And if you're putting it back on you just need to replace it with a nut.

You will need a 17mm socket to remove the bolts.


Once loosened, the brackets should slide off. You will not be using these anymore.

In the bag of hardware they've included, the larger pair of bolts, washers and nuts are the replacement. I ran into a problem when installing mine. I had to go to Lowes to buy a larger washer since the ones they've included are barely larger then the diameter of the bracket. I contacted APR about it, but they failed to get back to me.

Shown is what they included for this part, and the larger washer I had to buy.


This is what it looks like after installing it properly.

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You now need to remove the pair of nuts/bolts on each apron.





Removed


Now you should be able to slide the diffuser under the aprons. This isn't the easiest task since it puts a lot of stress on the 3M tape holding on the aprons. Mine ended up coming off partially. There is a problem though. You may be able to tell from the photos below, but because the diffuser does not conform to the shape of the bumper like the apron does, there is a point on the apron that pushes against the diffuser that makes it stick out unevenly. You can shave this off, or just live with it. If you leave it, it will more then likely scratch up the area that it contacts.





Now you can line up the holes from the apron and diffuser and bolt them down. I opted not to use the ones I pulled off and used longer ones since it makes the task MUCH easier. I recommend picking up a hardware kit like this one I got form Advance Auto.


Here's a better photo of the piece you probably want to shave down.

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Repeat to the otherside.

Now the task is to drill through the diffuser and bumper to make the diffuser sit flush to the edge of the bumper. Again, I didn't like the way APR wanted me to do this, so I came up with my own solution. The reason I didn't like they way APR's method is because although I can get about half the hardware in no problem, there are sections where I can not physically attach a bolt to the inside of the bumper since the diffuser is blocking the only access.

Use a piece of tape to help hold up the diffuser.


Here is the type of hardware I use. Self-tapping screws and clamps. You'll see why in the next few photos.


Pre-drill the holes through the diffuser and bumper. Be sure you measure and check 3x before you start drilling!!


After pre-drilling


I used a Dremel with a bit attachment for the next part. You can use the drill to do it too.




Attach the clamp. No access to the back? No problem. Thanks goes to Chris, my co-worker for this solution. After you line the diffuser back up, the screws will go right in. Don't worry about how it looks. It will be covered up by the diffuser.

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Now to secure the back portion of the diffuser with the self adjusting arms that were attached to the diffuser. You need to drill through the fender well. I used a 13/64th bit. I also got some lock washers to ensure they won't vibrate off.

First, line it up and mark where you will drill. You can adjust the arms by twisting the center cylinder.


After drilling


Lock washers I used


In and bolted down.


You need to tighten down the part that allows you to adjust the length.




Same thing only though the spare tire well.




Final

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Final Install Photos.