So I decided to install a 987 airbox in my 2000 S. It made sense to pull out the 986 airbox as I was doing a variocam wear pad job with the engine in the car and it seemed logical to pull it before the job so I would have extra work room. The 986 removal was awful. I loosened the intake manifold on the left side, bent up the motor cover attachment point on the drivers/front side and was having a really had time removing the airbox intact. I eventually cut it out in pieces. Given that the 987 airbox is much bigger I could not imagine the effort it would take to get it in. I was also worried about possible damage to the airbox or engine by forcing the larger box into the car.
Without the airbox in the way the variocam wear bar job was quite straightforward with the engine in the car. Not having the airbox in the way made me think that doing other jobs on the engine such as injector work or replacement of the aos hose that attaches on the 4-6 bank would be a breeze. So....to make installation of the 987 airbox easier and to allow future removal of the airbox for engine access I decided that I would cut the airbox into 3 pieces, install them one at a time and screw the pieces one to the other so that I could disassemble the box if needed at a future date. The three pieces each have an attachment point to the car and they are: 1) the side that is closest to the wheelwell; 2) the side next to the engine that attaches to firewall between the engine and passenger compartments; and 3) the portion of the box that includes the outlet and maf attachment.
I used a Dremel to cut the box up and the two large pieces (that did not include the outlet) I cut mainly on the molding seam. With the pieces out on the shop floor I fashioned attachment points using pieces of sheet metal so that I would have strong places to screw the parts back together. Where I could I riveted the pieces to the airbox. Some places I used bolts so that I could put it back together in the car. In a few spots I used sheet metal screws where nuts and bolts didn't work.
After several test fits to make sure that I could fit the parts back in and that the places where the parts attached would be accessible to tools I first put the side that attached to wheel well in followed by the piece with the outlet/maf holder and finally the side that is closest to the engine. I then screwed the pieces together loosely, bolted the pieces to the car and then did a final tightening down of all attachment points.
Once the airbox was in and everything tightened down I then sealed the joints/rivits/bolts/screws with high strength tape.
One mistake I made: the air filter is a tight fit in the airbox in its unaltered form. When I cut the pieces apart along the molding seam I unwittingly made the box about 1-3mm narrower. When I went to fit the filter in the only way I could get it in was by shaving a bit of the plastic off of the filter (with the Dremel). If I do disassemble the box again I will add a little width the the box to make it easier to get the filter in. The small portion of plastic that I removed doesn't look like it will affect the filter in any way.
There is an place on the wheelwell where the box attaches that other have noted interference from a hose/wire. That was easy to deal with: I put the piece on the wheel well, marked the interference point from under the car, took it out and used a heat gun to carefully melt the plastic enough to create a small indentation in the box. Tested the piece out and it was a perfect fit.
Others going back some ways have also noted that the outlet where the maf holder connects is a tight fit to the car body. That is true and it was so tight that I was only able to connect the maf holder by loosening the airbox bolts to the car and pull the box out while making the connection. Were I do a 987 airbox again I would make a cut on the inside corner of the outlet, bend the outlet so that the maf connection is moved an inch out from the body and then repair the cut with carbon fiber or fiberglass.