4.0L Cold Air Cowl Vent Intake
different types of snorkels, liked several of them (the Michigan Jeeper
Hummer style being my favorite except for the $300+ price tag) I also
liked K9's snorkel
I don't see
water over the hood hardly
ever...so being the cheap
jeeper that I am (and the wife's new practice of hiding the visa card)
I decided what I wanted to do based on these simple ideas.
- cooler air into the engine meant better performance.
- I didn't want something that could be smashed on the
- I liked the idea of it being stealthy
- I still needed to be able to ford 3 feet of water
- I had to be able to afford it by saving my lunch
And I saw a write up on
the web somewhere
during my travels but
there were no pictures (danged computers), so it was time to put on my
engineering hat and figure this out. If you ARE going to be fording
water over 4' deep then I suggest taking a look at K9's write-up
very cool home built snorkel.
My jeep is
from the cowl vent in front of the windshield.
If I don't show it to you, you'd never know it was there. It's
waterproof as long as I don't completely submerge the jeep up to the
windshield (not very likely in San Antonio).
- Another factory Air Tube (goes from the
throttle body to the factory
air box) - I bought mine online from e-bay for $35 - get the air box
too if you can - in case you jack up the old one or if you ever want to
- Two 2.5" PVC electrical box connectors
with nut (the gray kind is
fire rated), available at home depot electrical department. Test fit
them to the tube ends to ensure a tight fit.
- small piece of sheet metal (you will
need a 6 inch x 5 inch piece)
- one 2.5" metal plumbing joint sleeve
(lose the rubber insert)
- metal primer or paint (we don't want any
- 2.5" hole saw - bimetal.
- a tube of silicone RTV
- riveting tool and rivets (duh)
- standard hand tools
- hack saw or pvc saw
- tin snips or something to cut the sheet
- metal file
- a set of drill bits and a drill
- safety glasses (wear them!)
- good set of gloves for working with
First remove the
factory air box and air tube. Give the factory air box
a good cleaning (unless your purchase of an air tube came with an air
box also) and we will modify this first so the RTV can dry. Carefully
cut a 6 inch by 5 inch piece of sheet metal and then trim it so that if
fits the end of the box to cover the old intake hole where the air horn
was located. (safety first, where your gloves and glasses when working,
you only get 2 eyes and sheet metal is sharp!)
this onto the air box and if it looks good file the edges,
give it a good layer of silicone of make it air tight and put it in
place. Drill 8 to 10 holes and rivet the cover in place (I put 5 around
the outer edge and then another 4 very close to the old air horn hole,
then silicone over the rivets. Now set this aside so the RTV can set up.
location for the new
intake hole on the engine side of the air box (under the exit tube hole
in the top half of the box), by placing the one of the electrical box
connector nuts INSIDE the box It needs to have clearance for the air
filter, fittings, clamps when it is mounted. Be very sure to check for
alternator clearance as well! Measure it twice, cut once. Drill the
hole for the new intake using the hole cutter (keep the center scrap
piece for later). You may have to trim the threaded end of the
connector to allow for a tight fit. I took ½ inch off of mine
with a hack saw. Trim the excess to allow for a smooth physical
connection. RTV the nut and the connector where they will contact the
box and then assemble and set aside to allow for the RTV to set up.
Remove the cowl from the
vehicle. First remove the wiper blades by folding them away from the
windshield. Pull the locking tabs from under the wiper blades. Pull the
blade assembly straight away.
4 screws along the top of the cowl, remove
the 1 screw in the cowl vent.
hood, pull the rubber seal from top edge
of the firewall, and
remove the 2 cowl screws at each end of the firewall.
Put the hood back down and
carefully lift the leading edge of the cowl, then pull the cowl clear.
Notice the large drain under the center of the cowl, this is where the
water drains when it enters the cowl, on the passenger side you will
also see the fresh air intake for you have an a/c unit.
scrap plastic cut from the air box as a guide determine where you will
be cutting the hole in the firewall for the air intake (now it gets
FUN!) you want to be just left from the grounding screw in the firewall
as you look at the screw head in the engine compartment and low enough
to allow for clearance below the lip of the firewall and the ground
screw. Also check inside the cowl for clearance of the electrical box
connector nut (again you may have to trim back the length of the
threaded end to allow for a tight fit when installing this connector).
This is also a good time to create a little space by removing the wire
loom clamps that hold the wiring harness in place (and in your way) and
then releasing the connectors in the center of the firewall and
relocating them under the metal ledge (be careful to not damage the
it again and check for
clearance again, you only get one shot at this one! now it is time to
drill - no turning back!!!! Make your hole in the firewall, clean up
the edges with a file, mask it and give it a couple coats of paint or
primer to stop any rusting. Make sure you allow the primer to
dry...this is why I used the quick drying spray type (watch your
overspray and remember it sprays through the hole!). Test fit the
connector and then RTV all the connection points and assemble.
Holy Crap! You just made a 2.5"
hole in your firewall!!!
Take a break and let your heart rate come back down!
the lower half of the air box
Let's prepare the new intake
tube. Cut off about ½ inch to
either side of the oil breather connection - there is a base where it
joins the tube - I cut mine right at the ridge of that joint. Using the
metal joint sleeve temporarily reassemble the now shorter tube and
check for fit and clearance in the engine compartment. If you need to
trim the air tubes for length and/or fit now is the time to do it.
Disassemble the new tube and RTV the interior of the metal plumbing
joint sleeve (remember to remove the rubber insert). RTV the inside
edge of one of the tube halves. Use the joint sleeve to tightly join
the 2 halves. Back together. I put mine back at the same angles by
using the seam in the tube. Put the new tube aside and allow the RTV to
Really take a break now to
ensure all the RTV has set up before you begin making the mechanical
Assemble the new
short tube between the 2 new connectors you installed and tighten the
band clamps. I found it helpful to remove the clamp keys to allow me to
spin the clamps to more accessible positions. Assemble the filter and
top of the air box. Assemble the air box to throttle body tube. Reverse
the cowl removal procedures.
Double check all your
clearances and do a tool check.
Did you remember to take PICS?
Final thoughts and testing...
1. I have run a garden hose
full blast at the cowl vent with the engine running - no problem ... as
long as the lower end of the vent is not blocked it will drain water
2. I might test an air
scoop/air dam to see if it will affect highway performance. but on the
trail I want all that cooler air going down the intake.
3. I would have mounted the
connector closer to rear corner of the box
4. the size of all the tubing
is just under 2.5 inches...considering that the stock air horn is only
like 1.5 inches inner diameter I figured this is good.