Justifications
The stock intake system is too small for the 7.4L or even the 5.7L at full throttle and is a major constriction at most throttle settings in my opinion. If another supply line can be added without changing the existing, there will be two intake supply systems. All of this is in front of the air filter element, so it really doesn’t affect the smog system, that I know of. I decided to design a system to supplement the stock system and found all the materials at HomeDepot in the plumbing section (drainage, gutters and water meter boxes). Really got the idea after seeing a K&N system in a mag and thought I could do better and for less. This really needs to have the other end's restriction reduced too (change to dual exhaust).
Did this mod around 1997/1998 and picture is from addition of ~6" scoop in 2000/4/28.
Has two 90* elbows, 5"-4" reducer and 4" ID hose. Drainage pipe and fittings from Home Depot. There's tons of tie wraps in there that didn't show up in the picture. Can't remember where they are, but if you look VERY closely, you'll see some of them. Pipe was white, as they ran out of black (it's painted black). Had to buy 20 feet because they wouldn't cut it (only about 28" used).
Location of Air Intake Scoop and Hose
Scoop is just under the passenger side tow hook, snakes up next to the corner of the wheel well and punched a hole in the inner fender into the bottom of the filter box. The 90* elbow is long enough to go through and into the filter box.
At the inner fender sheetmetal edge, there is a length of rubber hose (1/4" or 3/8" OD vacuum hose slit lengthwise) around the holes sharp edge. Painted the sheetmetal with primer/finish before installing hose and used RTV adhesive inside the hose. It's all one piece after everything sets up. Elbow is really "tight" in that hole. Ditto the hole in the bottom of the filter box, except no vacuum hose, just tight fit.
Hose might interfer with those who have stock wheel offset and larger tires. Only when the tire is pointed inwards. Just a "might", as there is a lot of room on mine...but mine are 5.5"-6" farther out than stock (total track increase is about 11.5"-12".
Air Filter Box Modification
With the filter box top closed, it looks 100% stock. No telling that there is ram air mods.
Notice that there are water stains on the bottom of the filter box. It's from the rain mist that gets $ucked up into the filter box. There was a bunch of sand, pebbles, paper, bugs, etc in there that I cleaned before taking the picture. The white "dust" is from the filter element (factory "talcum powder" to allow ease of insertion into the intake flange on the right).
Scanning from the left:
Slot was two approx 2.5" dia holes with the web material between them cut out. Notice that the 90* elbow exits right there for a clear shot into the filter box. Small hole in front of them was my initial hold down bolt holding the 90* elbow in place while the RTV set.
Next is the stock 4"-5" dia runner fitment to the fender. There is an approx 2.5" boss that seats it to the filter box bottom (you'll see when you take this appart). Cut the end off and you'll have another inlet from the ram air 90* elbow into the filter box. The small thingie infront of that is the thing that lines up with the "C" channel mount unnderneath to the fender sheetmetal.
Next is another approx 2.5" dia hole that is stock. It too addes another inlet into the filter from the ram air's 90* elbow.
Next is the intake to the MAF sensor.
Notice the fender has duct tape covering production holes that allow hot engine compartment air into the stock intake (stock intake routs are into the cavity between the outer fender and inner fender). Thought I got all of them, but Mr WWS's first comment was that "you missed some". Sharp eyed Walter is someone I'd take to check out a used vehicle... :)
Notice DeathCool crud on the overflow bottle. Now have green and over fill till it's about 1/2" from top when hot.
Ram Air Intake Scoop Location
There is increased PSI and CFM where the scoop is mounted. The bumper has air spilling off of it and the taper of the lower section helps even more. The scoop gets even more air from these affects.
Home Depot had an approx 5"x9" drainage box that fit a 4" hose, but can't find it anymore and bought this 5" dia reducer. Again a bunch of tie wraps to stock holes under the bumper. There is room to snake a chain to the tow hook if you need to.
Further Modification:
Updated the ram air intake after the collision repair in early 2002 and added a 9"W x 4"H x 5" round scoop. as shown below. Will add a 2" x 1/16" aluminum border to the thing when time is available.
HERE IS HOW
This took me over 4 hours, but think I can do it in less than 2 hours now that I know how.
System is to intake from below the front bumper just under the passenger tow hook. 90deg elbow from there to wheel well running along the frame rail and wheel well up to the 90deg elbow just below the filter box. The tire/wheel does not touch any of this on my offroading (street is alloy 10x16-265/75-R16, offroad is stock rims-235/85-16... sold tires and will be getting something around 255/85-16 after I find & get specs). Since new system is under front bumper, there is chance it will be underwater, so leaving the OEM system avoids sucking in water, in addition to adding intake capacity. Scoop is the 4 to 3 inch reducer (really has opening of about 5.25 inch dia) and adds a mystery look (many have asked if there is a blower in there).
The rubber bumper is mounted on the bottom of the filter box. Remove and drill a hole in the bottom wall of the filter box, but DO NOT drill through the second wall. Drill a complimentary hole in the wheel well (there should be a wear mark from the rubber bumper). This will be the scribe datum. Tape up the area on the wheel well sheetmetal and scribe the 3.5 inch dia hole (diameter depends on the 90deg elbow you have and allow for the vacuum tube grommeting).
Filter box can now be cut by hand using the utility knife. There are two 2.5 dia holes inside facing the filter element. Cut the webbing between these two holes to make a 2.5 in x ~6 in slot, which will feed air into the box. Take the 3 in adapter to the fender and notice that it’s held in place by a 2.5 in dia boss sticking into the filter box. Cut out the boss bottom and it will become another 2.5 in dia feed into the filter box. There is another 2.5 in dia hole and you don’t need to do anything with it. Now you have qty 2, 2.5 in dia holes feeding air, PLUS a 2.5 in x ~6 in slot feeding air to the filter box. Now cut the 3.5 in dia hole in the bottom along the scribe lines using the rubber bumper hole as center.
Wheel well sheetmetal is very soft steel of approx. 18 gauge. Hole is complimentary to the ~3.5 in dia hole of the filter box. Better to cut too small and nibble to fit in the 90deg elbow & ¼ vacuum tube grommet. Spray paint the exposed bare sheetmetal and put the grommet in place while the two coast of paint is still soft, as it will "glue" it in place.
Now install the 90deg elbow, pointing towards the seam between the wheel well sheetmetal, frame rail and air bag sensor. The other 90deg elbow will be facing up from that corner and the flex tubing fits between them. There are lots of misc. holes that will be used to thread the tie wraps through to hold the elbows and tubing. The scoop is tie wrapped to a hole in the bumper just above the tow hook (there is a small piece of tubing between the scoop & elbow).
You need to tie wrap the tubing at several points to keep it as far away form the tire as possible. I used the hair dryer to soften and bend the tubing.
Lots of trail and error, but really not hard, just lots of work. I’m very pleased with the outcome and the cheapness of the whole thing. Heaven forbid, but if in an accident, it’s really not too much trouble to do it all again (and there was a 4x6 drain that they no longer carry, but will in the spring that I’m kind of thinking about changing to the scoop to).
Parts:
3 inch (nominal, 3inch ID & approx. 4 inch OD) drainage flex tubing (don’t use the perforated). $0.29/foot and need approximately 4 feet. Comes in black or white (black in stock when I priced and when finally buying, they only had white... it takes black primer paint well). They are in 100-foot rolls, but they usually have a roll from which they cut small amounts.
3 inch 90deg drainage elbow, $2.99 each and need two.
4inch to 3 inch drainage reducer (nominal, 4 inch ID & approx. 5.25inch OD). $1.99 each and need one.
Tie wraps (black, 12 inch or 18 inch or longer if you can get them). Need about 2 dozen (trial & error easily triples the number needed).
Masking tape. Build up a section where you will be drilling/cutting the 3.5 in dia hole to protect the surrounding area & it does catch some of the filings.
One can of black primer spray paint. Everybody has at least one can around, right? Spray any bare metal you end up with and make it several coats (I have a hair dryer handy to speed it up). $1.99.
¼ inch ID vacuum hose. Get the plastic kind (I used rubber and am going to regret... it’s not going to last as long). Split it down one side the whole length, as it will be used as grommet for sharp sheetmetal edge of wheel well hole. Need about 1incheshs. $1.79.
Misc. nuts & bolts, plumbers tape (I used sheetmetal from my 55gal scrape barrel next to the drill press/band saw).
Filter box has double wall bottom. There is about 3 inches between these two walls and there are three 2.5-inch diameter holes in the vertical section facing the filter. The stock intake routing is from a 1.5-2 inch dia opening behind the passenger side headlight. It then snakes into the passenger side fender just in front of the battery. Fender is double wall and feeds a 3-inch dia adapter, which fits, into the filter box. There is a 2.5-inch diameter boss holding that adapter to the filter box. If you cut the bottom of that boss, it adds another 2.5-inch diameter hole feeding the filter box from the new 3-inch system. There is a rubber bumper between the filter box bottom and the wheel well sheetmetal, that was used as the center for the hole between the filter box and the wheel well sheetmetal.
Tools:
Sheetmetal shears or jig saw. I have a Greenlee hydraulic punch, but just about anything that you can cut a 3.5-inch dia hole in #18 gauge sheetmetal will do.
Utility knife and several spare blades.
Misc. screw drivers, wrenches, pliers, hammers (both rubber mallet & ball peen), vice, grinder (nice if you have one), Band-Aids (I cut myself in all of these things), hand drill & bits, etc, etc.
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