Overview- Build a Ram-Air Intake using the stock air intake box and a 4 aluminum duct routed through the bottom of the box, down and over the top of the ...

Overview- Build a Ram-Air Intake using the stock air intake box and a 4" aluminum duct routed through the bottom of the box, down and over the top of the frame rail and then snaked forward to the bumper between the radiator and the frame cross-member; under radiator and over the 2" round steel cross-member. I used the 4 long rectangular bumper vents as my inlets and fabricated 2 scoops from 30 cal. military ammo boxes to bolt right behind the bumper vents. I attached the 4" duct to the right-side scoop then cross-linked the left scoop to the right with a short piece of 3" duct. I sealed the scoops to the bumper with thick weather stripping and sealed the ducts to the scoops (rammo-scoops) with thinner weather stripping. To finish off the mod, I made some changes to the stock air box by plugging the lower side intake hole that draws from the fender, and installed a flapper door over the top intake hole that I fabbed out of thin aluminum sheet metal. The flapper is there just in case the ram-air flow is strong enough to close it off and create positive pressure in the box. I have never been able to confirm if it closes or not.
To do this mod you'll need the following materials:
1) 1- 4" UL rated aluminum flex duct (the stuff that you can bend and stretch to about 6' long)
2) 2- pipe clamp bands for the 4" duct
3) 2- 30 Cal. military ammo boxes for the bumper scoops (10"x 3.5"x 7").
4) 1- 4" aluminum duct 90 degree bend.
5) Misc. 4" straight alum duct fittings for the ends but not required.
6) 1 - 3" aluminum duct 90 degree bend. I rotated the joints to make a straight/slightly bent cross connector piece for the scoops.
7) 2- 1/4" bolts and nuts about 1" long with big washers.
8) Several 8-10" long Plastic zip-ties to secure the duct.
9) 1 roll 3/8"& 3/4" EPDM weather stripping.
10) Optional -1/32" aluminum sheet metal for the flapper and plug.
Most of the materials shown below with the exception of the ammo cans, can be found at Home Cheapo. Obviously you need to be more creative to find the ammo cans (online/army surplus).

Tools you need: screw drivers, 3/8' ratchet & 10-12mm sockets or wrenches, pliers, tin snips, pop-rivet gun & 1/8" rivets, drill, 4"&3" hole saw bits (for metal), various other drill bits 1/8"-3/8".

Time it takes to Complete this Mod, 6-10 hours (get a couple of 12 paks). It'll be tough to complete in one weekend especially if you paint the scoops (recommended) and do some other optional things.
I'll split this into 3 PHASES: 1) DUCT INSTALL 2) AIRBOX MODIFICATION 3) SCOOP FABRICATION & INSTALLATION
The first 2 phases will take about 2 hours a piece, give or take; the last phase (scoops) takes the longest; about 4+ hours if you put 2 coats of paint on each scoop (drying/cure time).

Time to get started.
PHASE 1 - DUCT INSTALL
1) Remove the stock airbox and intake tube including the MAF sensor. I suggest unplugging the MAF sensor (airbox top) and storing it in a safe place. Once you get the tube off and the filter out of the airbox just pull the airbox up and away from the fender. It should lift out pretty easy since it is only held by three plastic retainers. Now is a good time to replace the old stock intake tube if you haven't already for a better flowing after-market one.
2) Remove the four bolts that secure the airbox support plate and take it out. Now you should see that underneath the airbox plate there is plenty of room to snake a 4" duct down beside the fender well to the frame rail after you move/remove the passenger-side horn out of the way. You can either totally remove it or reinstall it later in a different location.

3) Take the airbox (it's easier to do this now than later) and remove the short length of flared pipe on the bottom that creates a baffled inlet (keep it for now). Use the 4" hole saw and your drill to make a 4" hole in the bottom of the airbox so that the duct will fit in it and not interfere with the mounting plate attachment points and the wheel well liner attachment. underneath. In hindsight, I would have put the hole more in the center of the flat bottom section in the airbox instead of tight to one side to avoid the bracket below. In the spot I drilled the hole, the duct did not clear the wheel well attachment and I had to trim the fender attachment to keep it from gouging the duct. Take note that you don't want the hole in the back part of the airbox that has a sloping bottom so its best to start drilling from inside-out or top-bottom. After you drill the airbox bottom, put the mounting plate on the box and transfer the hole location onto the plate and drill through it as well.

4) Take one end of the aluminum duct and stretch out approx. 4" until the metal is semi-smooth. Insert that end into the plate and airbox together. The duct should fit pretty tight in the hole but will slip through the plate into the airbox. After you've checked that the duct will fit, adjust the amount of duct inside the airbox so that you have about 1/4"-1/2" extended off the bottom of the airbox, then mark the space between the plate and the airbox with a marker (outside and underneath). This space is where you will wrap a wide band of weather stripping around the duct and install a band clamp to seal it later. After you have a mark where you want it, take the airbox and plate off the duct and set them aside.
5) We're almost ready to start routing the duct to the bumper but first, remove the passenger-side horn, then remove the plastic skid cover from the underside of the truck front-end (under the radiator). It is held in place with about 5 bolts (keep it to be re-installed). Take a good look at where the duct is going to be routed down beside the fender-well and then pre-bend the duct a little at the bottom to get it aimed in the right direction. The duct will drop down on a forward incline to clear the fender well, then turn about 90 degrees towards the engine compartment. Find the space above the frame rail where the duct will clear. You might have to move the transmission cooler lines to the side of the rail to make room.
6) When you're ready, drop the duct down beside the fender well and poke it over to the rail crossing spot. Like this:

7) Keep working the duct down and over the frame rail carefully so that you don't damage the duct. Tip: Strectching the duct out and smoothing out the walls will make it fit easier but will also make it easier to damage so be careful. I would not strecth it out completely but if you do, you can collapse it again. Also, it was better to pull it through from the underside once you get it started over the frame rail. This process can be made easier if you remove the wheel well liner.


8) Now the duct should be inside the engine compartment down low. Easy right! When you get 2/3 of the duct worked through to the engine compartment side of the rail, that should be enough to reach to the bumper.
9) OK, go back to the topside under the hood and get the airbox mounting plate. Feed the marked end of the duct through the plate and set the plate back on the support bracket. Bolt the plate down and adjust the duct so that your mark is just above the plate. Wrap a piece of weather stripping around the duct at the mark and put one of the band clamps on top of the stripping then tighten it down until the weather stripping is compressed about halfway (use your best judgement on how tight to make it).
10) With the duct secure on the top, get back under the truck and finish stretching the duct across under the radiator until you get to about the center where the airbag sensor is located.

The airbag crash sensor is the small black box with a yelllow plug under the radiator. Push the duct by the sensor and over the top of the round steel tube frame brace towards the bumper.
11) Feed enough duct between the airbag sensor, radiator and pipe brace to reach the back of the front bumper.
12) Install zip-ties along the entire length of the duct wherever you can to secure it in place. Phase 1 Completed!

PHASE 2 - AIRBOX MODIFICATION
Before you re-install the airbox on the support plate there are a few changes to make.
1) Plug the small inlet in the lower side of the airbox. To do this, I used the flared plastic pipe that was removed earlier to trace a pattern on aluminum sheeting and cut the shape out with tin snips. You can use whatever you want to make a plug. I used super glue to fasten the plug.
If you are going to make a flapper/check valve for the upper inlet, now's the time. Note: You could omit the flapper and either plug the upper inlet or just leave it open.

2) Cut a piece of cardboard roughly the size of the inlet but oversized, shape it to cover the inlet hole curve and trace the hole on the cardboard from the outside of the box. Then make the tracing 1/4" larger on the two short sides and the bottom but do not change the top. Change the bottom two rounded corners to square corners with a straight edge. The top side of the flapper must clear the air filter so leave the traced edge as is.
3) Cut the card board piece on the new lines to make a pattern for the flapper. Place the flattened out cardboard pattern you just cut onto aluminum sheeting and trace it.
4) Cut the shape out of the aluminum with tin snips. Drill a small 1/16" hole in each lower corner of the aluminum flapper.
5) I used small I-hooks to make the flapper hinge at the bottom by cutting the I-hook to look like a sideways question mark.
6) Put weather stripping around the edge of the large inlet hole inside the airbox. Place the flapper door over the inlet hole align it over the weather stripping and bend it to shape.
7) Finally, mark the 1/16" holes in the flapper onto the airbox with the drill bit in your hand. Spin the bit with your fingers and it will make a divit. Drill the divits enough to screw in the I-hooks that you cut and leave the gap you cut facing down. The flapper should slide onto the hooks and hinge freely up and down to cover/uncover the inlet. Like this:

8) I made a stop out of a piece of 1/2"x 1/16"flat stock aluminum bar to keep the flapper from swinging down to far and falling off the hooks. Drop the air filter into the box and tilt the box to make sure the flapper swings clear past the filter. If it doesn't, trim a small amount off the top edge until it does.
9) OK, re-install the airbox over the duct and onto the mounting plate to complete PHASE 2.
In the previous picture you can see that I used a duct end coupler to terminate and clean up the duct end, but it's not really necessary. Up to you...

PHASE 3 - SCOOP FABRICATION & INSTALLATION
1) Remove the ammo can lids and latches. This is much easier to type than it is to do. The ammo can lid hinges and latches are spot-welded to the can so the best way to seperate the welds is to partially drill the divit at each the spot weld with an appropriately sized drill bit. Try not to drill all the way through the metal. You only need to weaken the spot weld so it will break off easy. Pry the lid hinge and latch with whatever you have that works; I used my punch set chisel and the welds popped off nicely. You won't need the lids or latches; trash 'em.
2) Take the naked ammo can and cut it diagonally from top to about 1" off the bottom something like this; see photo below. The short side will be to the outside and the taller toward the middle. Obviously the open ends will cover the bumper vents.

Cut both cans the same way with the snips, they will be opposite pairs when mounted to the bumper or the tall ends will face each other. When finished, it will be neccessary to bend or bow out the short side about 1/4" so it will just fit snug around both vents.
3) Time to go ahead and remove the front grille. If I remember correcty, there are 4 phillips head twist lock fasteners, 1 small bolt at the hood latch and a snap fastener at each end of the chrome band that just pull out; carefully. Results are a naked front end.

4) After you get the grill off, remove the plastic air deflector that sits flat behind the bumper vents and in front of the AC condenser. Chuck it; you won't need to re-install it.
5) Take the sculpted ammo cans and fit them to the bumper vents from the back. You will have to manuever the scoops just right to fit them into the space but they will fit. The left scoop will be slightly more difficult to fit but it will go with enough patience and force. The scoops may need a little trimming up to fit.
6) When you get the scoops fitted like you want, mark which one is left and which is right. The right scoop will need a 4" round hole in the bottom for the duct exit. Then the tall narrow sides of each will need a 3" round hole for the crosslink duct.
7) Trace the scoop outline on the back of the bumper as best you can with a sharpie or whatever you can fit in there. Then apply weather stripping all the way around as follows: Top edge gets 1 layer of stripping, bottom edge gets 2 layers and the sides need to taper from 2 layers to 1 layer; give it your best but it doesn't have to be completely airtight.
8) Now that the weather stipping is in place check the scoop fit one more time and get a helper to mark the top bolt holes that you will need to drill in the scoops for mounting. The two bumper flanges on the top are convieniently over the new scoop location and are the anchor points. Here:

9) Use the 4" hole saw to cut the hole in the bottom of the passenger-side (right) scoop, then drill the 3" holes near the back or bottom of the long side of the scoop the same on each one. Finally, drill a 1/8" hole or smaller, in the bottom, back corner of each scoop to drain any water out due to rain or whateva.
10) When all scoop fab is done remove any rust with steel wool and paint generously; 1-2 coats of the under coating paint.

11) Attach the 90 degree duct bend fitting into the sccop by first removing the non-crimped end section of the bend (drill out the rivets), insert the flared end of the joint into the scoop hole and re-rivet the bend.

Nice write-up! Always enjoy these well written DIY posts with lots of good pictures. Have you noticed a big change in power/responsiveness since doing the mod?

One thought I had was to maybe use PVC pipe rather than the duct pipe so it would be a smoother airflow. Possibly even some large tubing so you could bend it easily as well.

Nice job

Thanks guys!! I've been working on the DIY for a while and finally posted it but it's not 100% complete. I need to complete the scoop install and duct hook-up portion at the end. It's close though!

camfire87 wrote:Nice write-up! Always enjoy these well written DIY posts with lots of good pictures. Have you noticed a big change in power/responsiveness since doing the mod?

One thought I had was to maybe use PVC pipe rather than the duct pipe so it would be a smoother airflow. Possibly even some large tubing so you could bend it easily as well.

Thanks! Yeah I had several ideas on the duct materials but settled on the flex alum because it was quick and easy. I wanted to see how it would perform first before getting fancy. The difference it makes is better throttle response and more power/torque at highway speeds especially when towing (at least seat of the pants feel). I'll probably go back and make improvements someday; such as PVC piping (although heat might be an issue) and I even thought of making those narrow bumper vents larger/wider.