First off, Saab uses a Bypass or recirculating valve.. - Saab NG900 & OG9-3 Bulletin Board - Saabnet.com
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First off, Saab uses a Bypass or recirculating valve..
Posted by REM in Seattle (more from REM in Seattle) on Mon, 29 Mar 2010 10:45:11
In Reply to: Here's a dumb question that you can laugh at me for!, MikeMike, Mon, 29 Mar 2010 09:34:30
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Saab has always used a recirculating or Bypass Valve (BPV) instead of a blow-off (BOV) valve. A blow-off valve vents to the atmosphere, where as a bypass valve vents back into the turbo intake.
On your car a blow-off valve will not work as it completely confuses the Engine Control Unit (ECU). The Saab engine management system (your is a Trionic version 7 or T7 for short) makes fuel calculations based on the amount of air entering the intake. A BPV recirculated the air so the amount of air remains 'known', a BOV dumps air from the intake to the atmosphere and thus the amount of air is less than the ECU calculated.
The use of a different air intake filter, either a foam or cotton gauze filter in the stock airbox or a complete new intake pipe with a cone style filter, will allow more of the recirculated air noise from the BPV to be heard.
REM in Seattle
2005 Saab 9-3 Aero Convertible; Steel Gray metallic; 5-speed; 28,000 miles
1998 Saab 900SET; Silver metallic; 5-door; Automatic; 113,000 miles
1984 Saab 900T; Cherry Red; 3-door; 5-speed; 242,000 miles (RIP)
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