DIY Cold Air Intake

Posted by wret, Aug 14, 2005

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  1. wret

    wret Proven Member

    Joined Jul 3, 2003
    Bel Air, Maryland
    (for short route intercooler pipe)

    The biggest obstacle in construction a cold air intake box is matching the contour of the hood. Unless the box is contoured to match the hood with zero clearance, it's a waste of time. I devised a way to match the hood contour without expensive, hard to use contour gages.

    Sheet metal
    Pop Rivets or Screws
    Sheet Metal Screws
    Tubular Gasket Material (McMaster-Carr 12335A421 is perfect)
    Corrugated Cardboard
    Duct Tape
    Kebab Skewers
    Silicone Sealer or Gasket Material
    Sharpee Marker

    Tin Snips
    Rivet Gun (only if rivets are used for gasket attachment)
    Drill, Bits
    Jig Saw (optional but very easy to cut aluminum sheet metal)
    2-3 Small C-Clamps

    Making the Template
    1. Cut out cardboard shapes the dimensions shown in drawing. Be sure corrugation runs up and down in each piece. You can make one big piece if you have enough cardboard, If not tape the pieces together making sure the joints can bend to 90°.
    2. Remove air filter and whatever else is in the space in front of the fuse box.
    3. Test fit the cardboard box. You will need to trim the bottom of the rear and side pieces in a couple of places to match the contour of the intake area shelf.
    4. When you have a good fit, tape it securely to the shelf. Clean the shelf first if necessary.
    5. Test close the hood to test for clearance. Trim the box if necessary.
    6. Slide wooden skewers into the corrugation channels about 1 inch apart. You can cut the skewers into pieces if they are too long.
    7. Gently close your hood allowing it to push the skewers into the channels. Close the hood all the way and latch.
    8. Release and raise the hood. Observe the contours made by the ends of the skewers. There are a couple of areas where there are dramatic contour changes. Add more skewers in these areas to be sure you have a good gauge of the shape. Repeat as needed closing the hood each time.
    9. When your contour guide is complete, gently remove it with care not to move any of the skewers.

    Cutting the Box
    1. Lay the cardboard guide out flat. Run a strip of tape over the skewers to secure their positions.
    2. Use the cardboard guide as a template to draw the shape onto sheet metal. IMPORTANT: At the top contour line, reduce the height of the line ¼ inch for the entire length. This will assure clearance for the hood. The gap will be filled with a ¼ inch gasket. Draw in some mounting tabs at the bottom of each section.
    3. Cut the shape with snips or jigsaw.
    4. Bend at corners to form a box.
    5. Test fit box in the car and close hood to check clearance.
    6. Installing the gasket: It is much simpler to cover the contour edge with some foam tubing, pipe insulation for example. I think the gasket looks and performs better.
    7. To install gasket: Cut strips for cleats that will secure the gasket along the top contour. Most of them can be made with straight pieces but the front contour must be cut to match the line of the box. BETTER ALTERNATIVE (not pictured): 12335A421 from McMaster-Carr. It doesn't require a cleat to secure it. If you use this, skip steps 8 & 9.
    8. Clamp the strips to the top contour and drill near the edge where you will secure with rivets or screws. Don't do what I did: be sure the holes are close enough to the contour edge so that the rivets will penetrate the mounting strip of the gasket material. Camping force by itself will not be enough to hold the gasket in place.
    9. Sandwich the gasket mounting strip between the inside to edge of the box and mounting cleats and attach with rivets or screws.

    Fitting the Box
    1. Place the box in correct position in the car.
    2. Line up and mark the position of the intake.
    3. Cut out a hole for the intake and mounting screws.
    4. Mount the filter flange on the inside of the box and the MAS or intake flange on the outside. I recommend a gasket or sealant on both sides of the box.
    5. Place the box back in the car and drill at least 3 mounting holes through the box and shelf. Secure with sheet metal screws.
    6. Connect intake.
    7. Drive.

    Ron Tew

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    Last edited by a moderator: Jul 10, 2014
    B00stAddictedGsx and Defiant like this.

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