Bypass valve over BOV?
11-13-2007, 11:55 AM
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Bypass valve over BOV? i was wondering if anyone uses a bypass valve instead of a blow off valve? My 2005 Audi TT uses a bypass valve and ive alwasy thought how smart it is. Sucks that you loos that great sounding turbo pop, but you recycle the boost. Seems to really help my little Audi and i was wondering if any of you guys use one, or if any kits out there include them. Is there any down side to a bypass valve instead of a blow off valve?
11-13-2007, 12:07 PM
#2
BPV's are typically used for superchargers and BOV's are typically for turbos. Not all BPV's recycle the air, some vent to atmosphere just like BOV's. And those typically let out just as big of a 'whoosh' as the BOV's when you let off from a high boost blast. 
11-13-2007, 04:10 PM
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right, venting to atmosphere is where the noise comes from. I didnt know any of them would vent to the atmosphere, doesnt that defeat the purpose? By "bypass" i thought it meant to put, whats salvageable of the boost, back to the front of the system to pre-build the boost. I dont see how a bypass valve bypasses anything by venting it. Whats the difference between a blow off valve and these bypass valves that still vent it? I didnt even think of searching i really didnt think anyone would be using them cause ive never seen a thread on it. So i tried and search says its down.
11-13-2007, 04:30 PM
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By-pass is helpful on mass meter engines with the meter in front of the head unit. Once the air is measured, it re-circulates until the engine uses it so the calibration is not effected. It also is used in some systems to keep things quiet, so you can sneak up with your power adder and stomp them!!
Kurt
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11-13-2007, 07:21 PM
#6
THE difference between a BOV and a BPV is that a BOV is closed all the time except for when you let off the gas all of a sudden then it opens for a second to relieve pressure. A BPV is open all the time until it sees no vacuum (boost)- then the boost holds it shut. As soon as you let off the throttle, it opens back up and stays open because any vacuum on it keeps the valve open. The fact that it releases to atmosphere has nothing to do with it. I'm pretty sure there are just as many people here using a BPV as there are using BOV's. Like I said, BPV's are mainly for supercharged cars and BOV's are mainly used by turbo cars. This is not always true, but a good rule of thumb.
BOV's are for turbo cars since they can spin freely and not create boost at high RPM's but no load. Since SC's are creating boost relative to the engine RPM regardless of load, they need a relief for all the excess air. If that air is not used by the engine, it will cause back pressure and puts stress on the blower and can dramatically decrease bearing life, etc. Hence the need for a valve open all the time except for when you want to build boost.
BOV's are for turbo cars since they can spin freely and not create boost at high RPM's but no load. Since SC's are creating boost relative to the engine RPM regardless of load, they need a relief for all the excess air. If that air is not used by the engine, it will cause back pressure and puts stress on the blower and can dramatically decrease bearing life, etc. Hence the need for a valve open all the time except for when you want to build boost.
