Through the good advice of Chick Wells, I have posted my airbox
drawing to a server. The link is:
The picture is for the posting to the vwpassat group for modifying
the airbox for the B4 model but may be pertinent for other
The text is as follows:
After some study of what other people have do to modify their
airbox, I think I have come up with an easy, straightforward
method for increasing air intake flow while making sure it wasn't
hot air from the engine side. I put an assembly of 1 ½ " PVC
plumbing materials into place to draw cool air. Note : the type
of PVC used was Schedule 40 which is white, not the heavier
Schedule 80 which is thicker and is dark grey. The white stuff
fits, the grey doesn't because of the thickness.
The whole job took about 2 hours.
Many of you know the present airbox has two intake points in its
stock version. The first is through the front of the airbox base
via a 'snorkel' that sucks air from behind the passenger headlight
and above the passenger wheel well. It is a fairly clean, cool
source of air. Once the air goes through the snorkel, the air
passes through a very fine, domed screen in the airbox base. It
is there to catch snow and ice crystals (from what I have
learned). A lot of other crap is caught there and can be very
restrictive to your airflow if not kept clean. The second air
intake source is through the rear of the airbox base. There is a
hinged flap with a spring on it and a stub which goes from the
airbox and points towards the engine. The function of this is to
bring in warm air if the snow screen gets clogged. It can be a
problem air source if the snow screen never gets cleaned of other
debris because then the engine is then always drawing in hot air.
Not good for performance.
The assembly of PVC pieces I made up inserts where the rear stub
goes into the airbox base. There are two advantages of this
method than others I have heard or read about.
1. Reversibility - The parts removed can be replaced easily if
you don't like it, need to get the engine tested by government
programs, plan to sell the car, etc. Many other people advocate
cutting holes into the airbox base but I didn't want to do this.
Several after-market air intakes (P-flo and others) remove the
airbox but suffer then from warm air intake.
2. Can be done with simple materials : three 1 ½ " PVC elbows,
about 10" of 1 ½ " PVC pipe: one hacksaw, a Philips screwdriver.
The hardest part was removing the complete airbox (temporarily)
because it is in a tight space. Manoeuvring it around is a bit
frustrating and it is a tight spot to slide it out.
Here is what I did.
Disconnect the upper portion of the Air cleaner box from MAF (Mass
Air Flow) intake section. 2 large clips. Wiggle the section
apart gently. Don't lose the large O-ring.
Remove the upper portion of air box (4 clips). This is good
practice for changing your own air filter!
Remove air filter element
Remove the snow screen in the bottom front of the air box. Do
this by removing the two Philips screws and sliding the screen
assembly upwards. Either clean and replace it or leave it out
.......... your choice.
Remove the air intake snorkel. This is the piece that led into the
snow screen. It is just pressure fit into the front of the
airbox base. Slide it out to make some room to manoeuvre the
Remove rear spring loaded flap. It is in the bottom of the
airbox, opposite where the snow screen was. Do this by removing
two Philips screws and slide out the flap assembly. We want to
remove the small tube that goes from the airbox towards the
engine. It is about 6 inches long. Unfortunately it is secured
with two screws which are almost impossible to get out without
removing the airbox base. If you can find a way it will save the
next 2 steps which are difficult, mainly the removal of the airbox
On the rear of the airbox base, there is a purge regulator valve
that clips onto the box. It has an electrical lead connected to
it. You may want to unclip it. The valve is attached with a
rubber ring. Just slide it off (it is pretty tight so it will
take some force).
Now some tricky bits! Remove the rubber retaining ring which
holds the box base to the frame. It is like a heavy duty rubber
band and it is on the drivers side of the airbox base. Get a
flashlight and you will see it. I used a coat hanger and hook
onto it and stretch it to release it from the upper tab on the
airbox base. The airbox is 'attached' to the frame on the
passenger side of the box by an insertion bump which slides into a
hole on the frame. You won't see this until you slide the airbox
out. Make sure you move the AC hoses and other small hoses to the
sides to give as much access as possible. Lift the airbox up
from the side closest to the engine. After cursing and scraping
your knuckles a bit you will eventually get it out.
Now that the airbox is out you can remove the warm air intake
tube. Do this by removing the two Philips screws which you can
now see and have access to. Yes, this is why you needed to
remove the airbox base!
Now put the airbox base back in (more cursing and knuckle scraping
here). Relocate it into the frame on the drivers side and onto
two pins on the frame near the engine. Put the heavy rubber band
Now the PVC. It is all 1 ½ " (schedule 40) material. Do all
cutting and fitting dry, no gluing at least until you have
everything just right. When you cut the fittings and pipes
(hacksaw works fine), clean off any burs and sand the edges
lightly. I will describe the orientation of the fittings as best
I can now but I will take some pictures and scan them at a later
date. Insert one PVC elbow into the hole where the warm-air
flap was (rear of the airbox base towards the engine). It fits
perfectly with pressure. The elbow (open end) should face
directly upwards when you have it in place. Cut a very small
piece of the PVC pipe (about ¾ to 1 ") and insert it into the
elbow (previous step). Push the second PVC elbow onto the small
stub and turn the open end towards the passenger side of the car.
Another pipe piece will be cut (about 9 to 10 ") and inserted to
run along the rear of the airbox base towards the passenger side.
This is analogous to the air snorkel on the front of the airbox.
You could quit there but I added another PVC elbow pointing
forward. I did this because I noticed that some road crap can
get spray up from the wheels into this general area. There is a
small hole there where the wheel well plastic joins the frame.
This is the general set-up!.
You will need to play around with cutting and fitting to get it
all perfect. I did need to trim the initial two PVC elbows a
little so that the whole assembly could pass beneath the Mass Air
Flow properly. The elbows must be very tight together when you
are done. This is why the PVC insert was so short. All in all,
it didn't take very long to cut and get the assembly done. Way
more time was spent getting the airbox out.
Put the air filter element back in. If you want a throatier
growl to your vr6, you can remove the resonator out of the inside
of the airbox upper portion. This has been discussed before.
Put back the airbox lid (4 clips). You may need to slide the
PVC assembly out a bit to get the rear clips on properly and then
just pressure fit it back into the airbox base.
You are done.
Sorry for the long post but I thought this may help some of you
who have been considering it like I have and didn't want an
irreversible method. All parts can be put back in place with