DIY: High Flow Stock Airbox (Swiss Cheese Mod)

This is a great, simple, effective, and free mod that any owner of any model year can take advantage of. The plan is to get the most flow possible from the stock airbox setup while keeping a stock appearance. Great for all the sleepers out there, or those who want to leave the stock parts but optimize their performance.



The way the airbox works is that it has a dirty side (the bottom) a filter, and a clean side all in a sandwich. As such, we can open up the dirty side to allow more air in, while still channeling all the flow through the filter and leaving the upper airbox untouched.

Here's what you'll need:
- 10 mins
- cordless drill
- flathead and phillips screwdrivers
- new high flow filter (k&n or other, optional)
- MAF cleaner (optional)
- hole cutter bit (1")



Lets get down to work!

1. open the hood

2. disconnect the MAF wiring - pull up on the gray tab then push in, depress the black button and pull out. these are security tabs and are VERY easy to break if you muscle them too much.

3. loosen the MAF to airbox clamp (flathead)

4. undo the upper airbox bolts x 4 of them - they stay in the housing and don't come all the way out (phillips)



5. remove the upper airbox by pulling it up and away from the engine, sliding it outta the clamp on the MAF

6. remove the old air filter and set aside if you're gonna reuse it

7. now we can see the object of our project - the lower airbox housing. the housing is attached to the bracket by three rubber grommets on the bottom of the box (two are indicated by the red arrows). grasp the lower airbox firmly near one of the grommets and pull up sharply. it should pop right out.



8. notice how the two stock inlets are only a few square inches? time to get drillin and open her up! use the hole cutter bit to cut a bunch of holes in the sides of the lower airbox housing, taking care not to break any of the tabs or mess up the inner air conduit. you should have plenty of room to drill at least 12 1" holes around the sides and front of the lower airbox. keep in mind that the filter protrudes down about an inch so make your holes at least this far from the top lip of the box.

9. once you're satisfied with the drilling, put it all back together. line up the three grommets first, then push down firmly above each one. you should feel them "pop" back in, and the lower airbox should sit in there snug once again.

10. put your old filter back or throw in the new high flow one. if you can see a lot of the filter protruding through your holes, you drilled too high up. not a big deal, but too late now!

11. reassemble the upper airbox and reconnect the MAF. this is a great chance to clean the MAF btw (take it off the car duh . . . don't spray MAF cleaner into your intake).

12. start her up, notice the slight increase in throttle response, torque and smoothness at high rpm, and a touch of intake noise.

but, now won't you get bigger chucks in the air box, leaves etc? Then they will just clog the filter. no?

well, the stock holes are a few inches in diameter - each of mine is only a 1" hole. also, all of the extra holes are basically in the engine bay, and don't have snorkels to the outside like the stock inlets. as such, the extra debris, if any, should be minimal, and you're not gonna get any larger stuff than you can already fit through the stock inlets.

I've done and seen this done on many cars - not really an issue

I would imagine that if it ever did become an issue you could easily glue/silicon/whatever a screen cover over the holes with little effect on your new airflow.

SOLD! I'm doing it.

I suggest that the stock fender snorkels don't have the appropriate diameter to keep up with flow at the MAF, and are therefore a restriction - here's some quick math to support the premise:

diameter of MAF inlet = roughly 4", so radius is 2"
area of a circle: A = pi*r2, so A = pi*4 = 12.5663706

our holes have a radius of .5 inches, which equals an area of 0.785398163"

so . . . 12.5663706 / 0.785398163 = 16 (1" holes required to equal the area of the MAF inlet)

it doesn't take a genius to see that the stock inlet snorkels do not even come close to the equivalent area of 16x1" holes so you need to add a few - in other words, in stock config, your MAF is capable of outflowing your airbox at high rpm- so vent that thing up!

ypsetihw said:

diameter of MAF inlet = roughly 4", so radius is 2"
area of a circle: A = pi*r2, so A = pi*4 = 12.5663706

our holes have a radius of .5 inches, which equals an area of 0.785398163"

so . . . 12.5663706 / 0.785398163 = 16 (1" holes required to equal the area of the MAF inlet)

it doesn't take a genius to see that the stock inlet snorkels do not even come close to the equivalent area of 16x1" holes so you need to add a few - in other words, in stock config, your MAF is capable of outflowing your airbox at high rpm- so vent that thing up!

Click to expand...

I'll take your word for it

While it might not take a genius - it aparently takes more than my public education to see more than just a jumble of numbers.

Nice, free mods are always welcome here!

nice! i was just about to attempt something like this then i found your thread and well it will be done saturday plus i love the math back up

just for a reference, this works lol just in case anyone was on the fence about it

although I didn't use holes I just cut 2 big sections out of the dirty side of the box, but then again its dependent upon where you live, I don't have that much debris that gets kicked up

much better throttle response