Access into the cabin is via the oval opening in the firewall where the AC lines and heater core lines enter the cabin. Using the 1” hole saw drill a hole between the lines in the black foam insulator material. Insert the 1” metal pipe end of the sound tube into the hole. Inlet pipe and possibly the throttle body may be removed for this installation.
With the sound tube installed in the firewall layout the sound tube and then mock up the inlet pipe to see and mark exactly where to drill. Mark and drill the bottom of the inlet pipe to 1 ¼” the second to the last step on the step drill. Intake design and material may vary, but all will be drilled in the same manner. Clean the pipe and edge of hole and insert the grommet. Use lube or WD-40 on the inside of the grommet and insert the short end of the 90 hose barb until it’s seated then pull it down until it stops. Install the other end of the sound tube and re-install inlet and or throttle body.
Install the diaphragm cap on the inside of the car under the dash. Push the diaphragm cap over the end of the metal sound tube coming through the firewall.