Everything I've done here is before the filter. This is important, especially if your car has a Mass Air Flow Sensor.
This is my old setup which was the incoming air routed through the stock resonator of my 1995 civic VX. I was only able to increase the temperature about 20 degrees.
This is my modified lower filter box. The original intake hole is plugged with sheet metal with a 1/8" hole for drainage. A hole was cut in the front of the box and a three inch diameter aluminum elbow, from an old CAI system, was installed and sealed with silicone.
Stock resonator must be removed or the box can't be re-installed. On the VX I had to remove the inner fender well.
This is the "cut-out" that I am using as a mixing valve, they are $68us at Jegs.com. The bottom is connected to the hose from my exhaust manifold. To be honest, my car came with the “cutout” already installed, so I don’t know if the cable bracket comes with it or my Dad made it.
The modified box is now in place. The small wire runs from the temp sensor to the gage installed on the dash.
The cutout is attached to the elbow with a spectre silicone hose adapter from AutoZone.
Hot air hose attached to cutout
Hose intake at manifold is ziptied to the radiator fan shroud. And the manifold is enclosed with a flexible heat shield material (not sure where he got it).
The cable is run from the dash through a sheet metal plate. Whichever side of the cutout is routed to hot air will dictate whether cable in is hot or out is hot. Mine is labeled “IN/HOT”. Above the cable you can see my gage, it is battery operated so no wires except the sensor. These are available at Walmart for about $10.
I am already seeing around 50°f increase from ambient!