NG 900/9-3 3" Intake

Overview

The first stage in upgrading any car is to improve air flow into the engine. The Saab intake is quite restrictive and needs to be enlarged to reduce restrictions to the airflow.

• Cost: 5$ Pipe, $5 Adhesive/Sealant
• Time: 1 hr
• Difficulty: Moderately-Easy

Premise

Enlarging the stock New Generation (NG) 900 Turbo airbox inlet tube is easy and allows for far more air to enter the airbox. First off, the stock NG900 Turbo airbox has a 2 inch (51 mm) inlet tube that goes from behind the front right headlight/bumper to the airbox. There is a 2 1/2 inch (64 mm) outlet from the airbox to the turbocharger inlet. Therefore, the 2 inch inlet tube is the first restriction to more airflow.

Note that there is an opening in the front of the Saab NG900 from just above the right front fog light, thru the sheet metal, to the airbox inlet tube. This allows ample fresh cold air for the airbox intake. The front lip of the airbox intake tube can actually be seen by using a flashlight and looking up into the opening above the right fog light. If the vehicle is moving at all, the air will increase in pressure in front of the fog light, just like it does in front of the radiator, bumper, etc. This high-pressure air will move through the opening in the bumper above the fog light, through the large opening in the sheet metal to the airbox intake tube. In my case I replaced the stock 2 inch intake tube with a 3 inch intake tube for more air flow. The 3 inch intake tube hangs down into the air stream above the fog light even more. Add a K&N panel air filter in the airbox to eliminate even more intake flow restriction.

I replaced the 2 inch inlet tube with a 3 inch (76 mm) inlet tube made from PVC pipe. This changes the inlet tube area from approx. 3 sq. inches (20 sq. cm) to approx. 7 sq. inches (46 sq. cm). The front of the stock airbox is 3.25 inch across. The PVC pipe I chose is labeled 3 inch PVC Sewer/Drain and has a 3.25 inch outside diameter with a .080 inch wall thickness. This pipe is available in two types, a solid PVC and a newer style cellular core PVC with more impact resistance. The PVC pipe should be available at most home improvement or plumbing supply stores. I chose PVC because it is easy to cut, easy to shape with a heat gun, and is widely available. The use of PVC tubing in this application should not pose any hazard as the airbox inlet tube is far enough away from the engine heat to make melting or softening a non-issue, and if the PVC should break or shatter due to an impact, the engine air filter will keep any PVC fragments from entering the engine intake. I wrapped my PVC intake with fiberglass for more strength and impact resistance. Aluminum, Fiberglass, or Polypropylene (like a leaf blower tube), would also be good choices for the intake tubing. For the best results a smooth internal wall and a flared opening (bell mouth or trumpet shape)) at the front of the inlet tube is needed. These will help minimize losses in the intake flow.

Instructions

1. Remove the grill, right front headlight assembly, and right turn signal assembly.
2. Pay special attention to how the current inlet tube sits in relation to the bumper and headlight assembly. You will want your new 3 inch inlet tube to sit in nearly the same location.
3. Remove the stock airbox from the engine compartment.
4. Measure the length of the stock inlet tube from the front of the airbox to the end of the tube.
5. Cut a piece of 3 inch PVC tube about two inches longer than the measurement for the current inlet tube. Preferably the 3 inch PVC pipe you have chosen has a bell mouth (trumpet shape) on one end to accept the next length of PVC vent pipe. This bell mouth works very well as the inlet tube air in take end near the front bumper. Alternately, a bell mouth can be formed on the end of the tube by using a heat gun/hair dryer to soften the PVC tube and a funnel or similar tool to form the softened PVC tube. The bell mouth acts to reduce flow losses in the inlet tube.
6. Using the 3 inch inlet tube as a pattern, mark a 3 inch circle on the airbox over the current inlet tube opening. Be sure that the new opening will be below the lowest point of the air filter element.
7. Cut the opening for new 3 inch inlet tube. A utility knife, small saw, and a file or drum sander all work well.
8. Fit the 3 inch inlet tube to the airbox and check the airbox and inlet tube assembly for correct fit in the vehicle. Reinstall the headlight assembly to be sure there is enough clearance. Trim the airbox inlet tube opening, the inlet tube, and the ribs in the airbox as needed to get the proper fit.
9. At this point I stopped to paint the PVC tube black. This is for cosmetic reasons only, to blend in with the rest of the airbox and tubing. Use lacquer thinner to clean the 3 inch inlet tube prior to painting.
10. Clean the airbox where the tube will mount with lacquer thinner. Tack the 3 inch inlet tube to the airbox in a couple places using hot melt glue. The hot melt glue is just to temporarily hold the new inlet tube during the clearance check. Check again to be sure that the inlet tube will clear the headlight assembly. Then completely seal the inlet tube to the airbox both inside and out using Black RTV Adhesive/Sealant. Be sure to keep the water weep hole in the bottom of the airbox clear.
11. Reinstall the airbox, headlight assembly, turn signal assembly, and grill.
12. Obviously, this is just one step in improving the airflow to the NG900 Turbo. A K&N filter element and a low restriction exhaust are additional steps that should be taken. Dean has also suggested that the plastic silencer in the turbo intercooler inlet tube be removed, and that the abrupt edges in the throttle body transition housing (where the turbo intercooler outlet connects) in front of the throttle body be smoothed.