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These instructions work great for the 1994-1998 NG900 and the 1999 9-3. I have personally done this modification on MY1995, MY1998, and MY1999 vehicles.
REM in Seattle
2005 Saab 9-3 Aero Convertible; 5-speed; 500 miles
1998 Saab 900SET; 5-door; Automatic; 73,000 miles
MODIFYING THE FACTORY NG900 TURBO AIRBOX FOR A 3 PVC INLET TUBE.
By Rob Mustard (aka REM in Seattle)
Search word: rem_mod
Last updated March 10, 2003
Enlarging the factory New Generation (NG) 900 Turbo airbox inlet tube is easy and allows for far more air to enter the airbox. First off, the factory NG900 Turbo airbox has a 2 (51 mm) inlet tube that goes from behind the front right headlight/bumper to the airbox. There is a 2 1/2 (64 mm) outlet from the airbox to the turbocharger inlet. Therefore, the 2 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 should allow 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 factory 2 intake tube with a 3 intake tube for more airflow. The area of the 2 diameter inlet tube is approx. 3 sq. inches (20 sq. cm), while the area of the 3 diameter inlet tube area is approx. 7 sq. inches (46 sq. cm) or more than double the area of the factory inlet tube. Add a high performance panel air filter (like the K&N #33-2663, Amsoil #TS88, or ITG #WB-364 air filters) in the airbox to eliminate even more intake flow restriction.
The front of the factory airbox is approximately 3.25 across. The PVC pipe I chose is labeled 3 PVC Drain and Sewer and has a 3.25 outside diameter with a .080 wall thickness. Thin walled PVC electrical conduit would probably also be suitable. The standard Schedule 40, and DWV (Drain/Waste/Vent), 3 PVC pipes have a .210 thick wall and are 3.5 diameter, and so will be too wide to fit the front of the factory airbox. Thin wall 3 PVC Drain and Sewer pipe, or thin walled PVC electrical conduit 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 later wrapped my PVC intake with a fiberglass pipe repair kit for more strength and impact resistance. Wrapping the PVC pipe with a high temperature duct tape is another option. Aluminum tubing (like irrigation pipe), Fiberglass tubing, 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 are needed. These will help minimize losses in the intake flow.
STEP BY STEP INSTRUCTIONS
1) Start by removing 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 inlet tube to sit in nearly the same location.
3) Remove the factory airbox from the engine compartment.
4) Measure the length of the factory inlet tube from the front of the airbox to the end of the tube (mine was approx. 10 inches).
5) Cut a piece of 3 PVC tube 1 to 1 ½ inches longer than the measurement for the current inlet tube. The new 3 inlet tube will extend from the airbox the same distance as the old inlet tube. The remaining 1 to 1 1/2 inches will protrude inside the airbox. Preferably the 3 PVC pipe you have chosen has a bell mouth (trumpet shape) on one end to accept the next length of PVC 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 or 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 airflow losses in the inlet tube.
6) Using the 3 inlet tube as a pattern, mark a 3 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 inlet tube. I used a small jigsaw, a utility knife, and a course file, to cut and shape my new opening.
8) Fit the 3 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 inlet tube prior to painting. Alternately, the PVC pipe can be wrapped with a high temperature duct tape (like the aluminum duct tape) or fiberglass cloth. This will also help contain the PVC pipe in the event of a fracture.
10) Clean the airbox where the tube will mount with lacquer thinner. Tack the 3 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.
Obviously, this is just one step in improving the airflow to the NG900 Turbo. A high performance panel air filter (like the K&N #33-2663, Amsoil #TS88, or ITG #WB-364 air filters) and a low restriction exhaust (like the Saab Sport 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.
posted by 24.16.197...
REM in Seattle
2013 Volvo XC60 R-Design, Rebel Blue, 3.0L 6-cyl turbo, Automatic
2005 Saab 9-3 Aero Convertible, Steel Gray metallic, 2.0L 4-cyl turbo, 5-speed
1998 Saab 900SET 5-door, Silver, 2.0L 4-cyl turbo, Automatic
1991 Alfa Romeo Spider convertible, Alfa Red, 2.0L 4-cyl, 5-speed
1984 Saab 900T 3-door, Red, 2.0L 4-cyl turbo, 5-speed
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