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Old 07-18-2006, 11:00 AM   #1
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Default what does vented bov to atmosphere mean?

haha. ok so I am not a noob or anything, just never heard this. so I guess I have missed out about what it means. Can someone please explain, as I am about to install a turbo kit.
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Old 07-18-2006, 11:24 AM   #2
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VTA - Just means that it Vents to atmosphere (excess pressure from the Turbo) - The VTA's do not recirculate back into your intake.
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Old 07-18-2006, 12:31 PM   #3
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A VTA valve discharges air from the intake piping (pre-throttle) directly out into the atmosphere. A recirculating valve discharges it's air back into the intake system, between the air flow meter and the turbo compressor inlet.

The difference has primarily to do with what type of engine management is being used. A system which uses only a MAP sensor is fine with VTA valves. The idea being that since the ECU is measuring the pressure inside the intake manifold (post-throttle) it doesn't really know or care how much air is being dumped overboard before it gets to the throttle plate. You could remove the whole intake system up to the throttle plate and it would run just fine.

Systems such as ours which use airflow meters (be they flapper or hotwire) can have issues with VTA valves. The problem is that, during a vent condition, all the air that's being exhausted out the valve has already passed through the metering system, and the ECU assumes that it's going into the engine. The ECU adds what it believes is an appropriate amount of fuel, but since the air is in fact being wasted the result is that the engine runs rich during this period.

Recirculating valves solve this problem by keeping the system closed and reintroducing the air back into the turbo after the metering device. This way, the air gets measured once, and as it loops through the system it does not get measured again. So the airflow meter sees only the equivalent amount of air that's actually being ingested into the engine, and the fuel mixture is correct.
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