BPV and BOV operation.... - Saab Performance Bulletin Board - Saabnet.com
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BPV and BOV operation....
Posted by REM in Seattle (more from REM in Seattle) on Fri, 28 Apr 2006 23:40:58
In Reply to: Understanding BPV operation?, dudewithassab, Tue, 25 Apr 2006 20:25:47
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When you shift or let off the gas quickly when on boost, the throttle butterfly plate will slam shut. The air the turbo has forced into the intake will in turn 'bounce' off the throttle plate creating a pressure wave. That pressure wave is directed back toward the turbo compressor wheel , and unless directed else where, will slow or stop the compressor's rotation. This is bad for performance in that the turbo will have to spool up AGAIN in the next gear, and it can also lead to damage to the compressor wheel over time.
The By-Pass Valve (BPV) alleviates this problem by venting the charge air trying to enter the closed throttle body back to the the air intake just before the turbo. A BPV is virtually required on any vehicle that meters the air flwing to the throttle boby, such as the later 9-3 with MAF sensor.
The difference between the above mentioned By-Pass Valve and a Blow Off Valve (BOV) is the way it vents. The BOV releases the charge air to the atmosphere. The BOV requires less plumbing and may release very high charge pressures (like used in a rally car) a faster than a BPV.
REM in Seattle
2005 Saab 9-3 Aero Convertible; 5-speed; 9000 miles
1998 Saab 900SET; 5-door; Automatic; 83,000 miles
1984 Saab 900T; 3-door; 5-speed; 242,000 miles (RIP)
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