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re-circ diverter valve Vs. BOV on VRT


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from garrett site...

Blow-Off (Bypass) Valves

The Blow-Off valve (BOV) is a pressure relief device on the intake tract to prevent the turbo’s compressor from going into surge. The BOV should be installed between the compressor discharge and the throttle body, preferably downstream of the charge air cooler (if equipped). When the throttle is closed rapidly, the airflow is quickly reduced, causing flow instability and pressure fluctuations. These rapidly cycling pressure fluctuations are the audible evidence of surge. Surge can eventually lead to thrust bearing failure due to the high loads associated with it.

Blow-Off valves use a combination of manifold pressure signal and spring force to detect when the throttle is closed. When the throttle is closed rapidly, the BOV vents boost in the intake tract to atmosphere to relieve the pressure; helping to eliminate the phenomenon of surge.

Wastegates

On the exhaust side, a Wastegates provides us a means to control the boost pressure of the engine. Some commercial diesel applications do not use a Wastegates at all. This type of system is called a free-floating turbocharger.

However, the vast majority of gasoline performance applications require a Wastegates. There are two (2) configurations of Wastegates, internal or external. Both internal and external Wastegates provide a means to bypass exhaust flow from the turbine wheel. Bypassing this energy (e.g. exhaust flow) reduces the power driving the turbine wheel to match the power required for a given boost level. Similar to the BOV, the Wastegates uses boost pressure and spring force to regulate the flow bypassing the turbine.

Internal Wastegates are built into the turbine housing and consist of a “flapper†valve, crank arm, rod end, and pneumatic actuator. It is important to connect this actuator only to boost pressure; i.e. it is not designed to handle vacuum and as such should not be referenced to an intake manifold.

from what i understand after a bit of reading, the blow-off valve vents the excess intake air. where as the recirc/diverter flows it back into the intake pre-turbo.

i know that with the recirc you wont get the ptishh, but also that it can increase throttle response etc. wondered if people have got experiences of both on VRT's.

another factor is that you can get forge recircs for about £60 2nd hand...

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In simple terms:-

Mass Air based fuelling (OE ECU) - Recirc

Manifold pressure fuelling (Standalone) - Blow off valve.

Or, if you don't like blow off noises, you can use a recirc on both applications.

I can do you a nice 50mm Forge recirc valve if you want? Much better than the little 007P :-)

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