After reading this thread discussing the GXP airbox, , I decided to examine the airbox on my GXP and determine specifically what might be done to improve it. After examining the airbox, I felt there were 3 areas that could possibly be improved:

1) The tube that connects the 2 halves of the airbox is on the small side. The ID of the tube is 2 5/16s (about 59mm) at the smallest point. (This was not measured with dial calipers, but with careful checking and rechecking using a cardboard template). I’d be interested in an expert opinion on whether this size is less than optimal for a 275 horse N/A engine. After removing the air filter lid and the top half of the airbox, the tube can be popped out by simply lifting on it. The tube will come out along with part of the dividing wall. (see the 6th pic posted by ReallyAGXP in the thread referenced above, and you’ll see what I mean). At that point you are left with a flat opening that is a little wider at 2.5 inches, and definitely taller. The dividing wall could be further opened up quite a bit more, but if you do that, you won’t be able to return the airbox to stock.

2) The tube that carries air from behind the grill into the airbox is of reasonable size. So normally that would not concern me. However, I’m not thrilled about the fact that it’* up there pretty close to the headlight, and the headlamp harness is hanging down right in front of it. I pushed the harness aside, but I’m sure it’* back.

3) As mentioned in the previous thread, the accordion tube that connects the MAF to the TB has huge ribs that are not great for flow. It does need to be very flexible to accommodate engine movement. I may try to see if I can find a flexible inlet hose that might flow a little better.

So anyway, because it’* so easy, I popped out the tube the other day, and have been driving without it. I really can’t say for sure if the car is any faster. It feels a bit stronger, but I have to wonder if that’* because I want to believe it’* quicker. There certiainly does not seem to be any loss in low-end torque since the car lights the tires the same as before. Drives perfectly fine too. But hey, it only takes 15 minutes to pop it out, so someone else try and let me know. I’d rather not hack up my airbox, but I have a feeling that I am going to give into temptation and cut away the rest of the wall at some point. But I want to do either a dyno or track test stock first so I can find out for certain if there is anything to be gained here.

Why not just fab up some sort of CAI or FWI using some tubing?

It would take a lot of convicing for me to believe that a tube can be outflowed by a box, its just not logical.

Thats why you have a garden hose, not a garden box-like structure.

I may fab up a CAI at some point, and I did do that on my older vehicle. But this is a newer car still under warrantee. My main concern is relocating the PCM since it resides inside the airbox and is cooled by the inlet air. I want 100% rock solid reliability for this vehicle for now. But I would like to know what others have done with the computer when they went to a CAI.

The pcm doesn't need to be cooled, and will have no adverse effects from being left exposed.

There are dozens and dozens of them just like that on this Forum alone, and many more on others. The PCM is weather-proof.

As for me, I left a slightly modified portion of the bottom piece of my airbox in place, the part that in my application holds the PCM. I did have to do some hacking away on it though, which I would understand if you dont want to do. But you may have enough clearance to run some tubing and keep that portion in place, especially if you go with a CAI over a FWI.

Just do some looking around, take things apart, take measurements, brainstorm, all that good stuff.

Sure enough, I gave into temptation and cut the right side of the wall out. The car feels a little stronger, but that can be deceiving, and I cannot make any statements about performance gains until such time as I can verify them. I will be able to reinstall the right wall and tube with the help of some silicone to allow for reverse testing.

It is nice to know that I can do a CAI and not worry about the PCM. Gutting for now since it is free and easy.

What did you do exactly can you post some pics?

I apologize for not taking pics, the battery in my digital camera was dead. I will try to find time to open it up and take pics at some point. But it is really simple to do this, and there are detailed pics of the airbox in the previous thread. Once you remove the top half of the airbox, it’* all pretty obvious. But here is a step by step guide:

1) loosen the hose clamp where the airbox connects to the MAF.
2) There is a small hose (approximately 2” in diameter) that connects to the airbox. It just slides off.
3) Remove the air filter cover by loosening the 2 wing screws, tilting it up, and then pull it toward the fender to release the 2 tabs at the back.
4) This exposes the air filter, but the top half of the airbox is still in place. Loosen the 3 (or 4?) Phillips screws holding it in place, then gently lift the top half of the airbox off. Like the air filter cover, it has tabs that hold it in place on one side, so pull it toward the fender as you remove it to release the tabs.
5) At this point you are staring at the tube that connects the 2 halves of the airbox. Just lift up on both ends and it should easily slip right out, along with part of the wall that separates the 2 halves of the airbox.
6) Optional: With the tube removed, there is a ¼” hole in the bottom of the airbox where the tab holding the tube snapped out. OCD compelled me to seal it with a dab of RTV. Can you imagine all the hot engine air that ¼” hole could let in?
7) Now the tube is gone, but you’ll see that on either side of where the tube was the remainder of the wall is still in place. I removed the side of the wall closest to the fender. It’* pretty tight in there. I alternated between a 3” cutting wheel on a drill and a dremel cutting wheel on my die grinder. But hey, it’* plastic, so it’* still a piece of cake!

I did not yet bother with the other side of the wall because a) the PCM is still mostly blocking that side even if that part of the wall was gone, and b) air coming from that side of the box is going to have to make a hard turn when it gets to the airbox outlet. And finally c) the size of the original opening through the tube has been increased by a factor of something like 3 or 4, so it’* no longer a bottleneck.