Write-Up: Gutting the Stock Air Box

A very simple and inexpensive way to get a slight power increase is to remove your car's air intake box and take out some of the restrictive baffles and acoustic silencers to improve intake air flow. More air in = more fuel added by the car's PCM, which means more power is made. This mod is commonly referred to as "gutting the box", and it's only needed on '96 and up models ('95 came without noise-reducing restrictions). Here's how to do it:

STEP 1: Remove the cover.

- loosen the wing nut clamp on the rubber air intake tube.
- remove the tube from the air box, rotate the tube upward so you have some room to work.
- disconnect the two-wire plug from the air box. This is your IAT sensor.
- there are two plastic clips on the side of the box facing the engine. pop them open and the cover with come off.
- remove the filter. At this point, you could just add a K&N filter panel (use #33-2250 or #22-2086, they are both identical) or the filter of your choice for better air flow. Make sure you adhere the foam seal around the lip of the air box. If you want to open things up even more to hear some cool blower whine, proceed to the next step...

STEP 2: Remove and gut the box.

- there are two hex-head screws holding the bottom portion of the air box to the car. Use a socket wrench to remove the screws, then lift the box up and out of the engine bay.
- there is a piece of red plastic baffle held in with plastic welds. Cut or drill the welds, or just pull on the red piece until they break, then remove the baffle and then you'll see a light grey plastic thing with multiple chambers. Remove this and discard all pieces except for the two halves of the air box itself.
- if you have a Dremel tool, you can grind away the sharp opening in the cover where the intake tube attaches, and any other obstacles that might impede air flow.

STEP 3: Reinstall the box.

- Reinstall the bottom part of the box. It may be loose without the grey piece, so use a zip tie to secure the box to a part of the car. I drilled a small hole in the bottom of the box and looped the tie around a piece of metal below it.
- install your filter panel, then replace the top cover of the air box. Don't forget to plug the IAT sensor back in!

The nice part about this mod is that it takes only an hour to do, and you'll notice the difference instantly, but no one will suspect you've done a thing to the car because the air box will still look exactly the way it used to (stock).

Understand that along with about a few extra horsepower, you'll hear an increase in the sound level produced by the supercharger. In other words, your car will now make a distinct "whine" when you get on the throttle, yet during most normal driving you won't notice much difference.

For about $60 you can invest in a K&N high-flow air filter. The K&N is supposed to improve flow over the OEM filter, and it is reusable.

Pictures (Thanks Orca):

The airbox has two halfs, the "top" that attaches to the rubber tube to the engine, and the "bottom" that is bolted to the body.
Do both the red plastic plate in the "top"
and
The grey piece in the bottom facing the hole in the fender well
Both come out?
Yes, I read the fac, but it makes it sound like both the red and grey parts are in the "bottom" half, and in my Riv the red is in the "top" or lid.
Thanks,

Riv in Reno
now with gutted airbox.

both come out, the red piece is the most restrictive part. let us know what you think of it after you do that.
oh and get a new filter if you havent already, so you see the true gain of the mod.

New filter (Fram) in place, red plastic plate out and it is both more powerful and more "even" in feel through the rev range. I left the grey part in place untill I build a through the fender intake. It looks like the grey piece might help keep water or other debris from hitting the filter element. There were pieces of rubber, like a belt or tire in the bottom of the airbox ?!!!

Riv in Reno

rubber?? wierd. i think the grey piece is just to collect dirt and leaves, you will not have any problems with water. if you were going through water high enough to get on the filter then thats the least of your worries

Yep, rubber with fiber reenforcing like a belt or tire has. The sand, plant parts and unknown stuff was to be expected, but chunks and short strips of rubber??? I was thinking of water in the form of mist or drops might be deflected by the grey piece.

My wife took the Riv over the hill (that's Reno talk for going to Sacramento or other parts of the Granola Republic) So I'll get feedback on how the car is in rain and slush. Or snow...
The chains that came with the Riv are unused, the SAE type called for in the manual, and the right size. But the sales slip in the box was dated 1992???
"Let's do the time warp again..."

Riv in Reno

Riv in Reno wrote:

I was thinking of water in the form of mist or drops might be deflected by the grey piece.

Mist or drops will not be an issue. You could go through at least a foot of water without taking water in. Of course you should avoid that situation.

I imagine the rubber is road debris that was picked up.

quote: "Mist or drops will not be an issue."

Correct. Injecting a fine mist of water into the intake can actually have a performance-enhancing effect.

how does that work, by cooling the charge???
guess the humidity here isn't so bad after all...

Yes, but it has to be controlled. I believe the WRX STI has an OEM water injection system... works like N2O, but to a lesser degree.

Please don't inject water into your intake unless you know what you're doing.

I just did the airbox gutting, feels like a slight increase but it turned out the the noise level was hardly noticeable,which is good.

I would remove the grey piece if you haven't yet. As Racingfan said, the only way water will get to your filter is if you drive through a 2ft puddle and then you will have other problems. I noticed more a difference removing the grey piece then removing the red piece in my car.

96riv wrote:

I just did the airbox gutting, feels like a slight increase but it turned out the the noise level was hardly noticeable,which is good.

I noticed a pretty big difference in the supercharger whine after gutting the airbox.

Quote :

It looks like the grey piece might help keep water or other debris from hitting the filter element.

the grey baffle is a helmholtz resonator. Remove it.

WOW.........Honestly this was very helpful.......i did not know what a gutted airbox was? lol..........but i don't need to worry because i have a 95!

THANKS!

that grey piece(the piece being removed in the last photo), I left mine in, worring about sucking in water. Has everyone else removed that grey piece? Also has anyone heard about sucking in water? Should i be worried about sucking in water?

Well, I replaced my airbox with a tube that goes right down in that hole, with the filter installed below where your grey piece is. I've been running it now for 2 years, driving through some pretty hard rain and deep puddles:



(remove the grey piece, no water will come in unless you drive through a lake)

mayfair4life187 wrote:

that grey piece(the piece being removed in the last photo), I left mine in, worring about sucking in water. Has everyone else removed that grey piece? Also has anyone heard about sucking in water? Should i be worried about sucking in water?

its fine. I even cut out the venderwell plastic lining so there is nothing blocking the intake from the outsite environment except the actual filter itself.

dreww wrote:

mayfair4life187 wrote:

that grey piece(the piece being removed in the last photo), I left mine in, worring about sucking in water. Has everyone else removed that grey piece? Also has anyone heard about sucking in water? Should i be worried about sucking in water?

its fine. I even cut out the venderwell plastic lining so there is nothing blocking the intake from the outsite environment except the actual filter itself.

You don't have the lining at all? Do you drive in the rain with it?

SpaceBar wrote:

dreww wrote:

mayfair4life187 wrote:

that grey piece(the piece being removed in the last photo), I left mine in, worring about sucking in water. Has everyone else removed that grey piece? Also has anyone heard about sucking in water? Should i be worried about sucking in water?

its fine. I even cut out the venderwell plastic lining so there is nothing blocking the intake from the outsite environment except the actual filter itself.

You don't have the lining at all? Do you drive in the rain with it?

yes. no problems. after you do this, you can reach your hand into the fenderwell and actually touch the filter. But, you have to reach up there a ways. Water could get in there, but its be alot harder than getting water into a cone fenderwell cold air intake.(which is considered the best air intake setup)

dreww wrote:

SpaceBar wrote:

dreww wrote:

mayfair4life187 wrote:

that grey piece(the piece being removed in the last photo), I left mine in, worring about sucking in water. Has everyone else removed that grey piece? Also has anyone heard about sucking in water? Should i be worried about sucking in water?

its fine. I even cut out the venderwell plastic lining so there is nothing blocking the intake from the outsite environment except the actual filter itself.

You don't have the lining at all? Do you drive in the rain with it?

yes. no problems. after you do this, you can reach your hand into the fenderwell and actually touch the filter. But, you have to reach up there a ways. Water could get in there, but its be alot harder than getting water into a cone fenderwell cold air intake.(which is considered the best air intake setup)

Oh ok. I thought you had a fenderwell intake. Didn't realize you just had the k & n drop in with the gutted airbox.


How does that work out? What kind of temps are you getting?

SpaceBar wrote:

dreww wrote:

SpaceBar wrote:

dreww wrote:

mayfair4life187 wrote:

that grey piece(the piece being removed in the last photo), I left mine in, worring about sucking in water. Has everyone else removed that grey piece? Also has anyone heard about sucking in water? Should i be worried about sucking in water?

its fine. I even cut out the venderwell plastic lining so there is nothing blocking the intake from the outsite environment except the actual filter itself.

You don't have the lining at all? Do you drive in the rain with it?

yes. no problems. after you do this, you can reach your hand into the fenderwell and actually touch the filter. But, you have to reach up there a ways. Water could get in there, but its be alot harder than getting water into a cone fenderwell cold air intake.(which is considered the best air intake setup)

Oh ok. I thought you had a fenderwell intake. Didn't realize you just had the k & n drop in with the gutted airbox.


How does that work out? What kind of temps are you getting?

I'll have to get back to you on that. I can only read it when scanning...but I'll have to convert it from C first.

Will gutting the airbox increase or decrease fuel consumption under normal driving conditions ?

Will gutting the airbox increase or decrease fuel consumption under normal driving conditions ?

It should slightly decrease fuel consumption under equal driving conditions.