Blow off Valve Question
The Diaphragm / Piston has to have a reference for the back side.
The front side's reference is the intake manifold. So the back side needs a reference and we can choose from either atmospheric pressure like most all aftermarket BOV's have or we can choose to use boost pressure, which the stocker uses.
Lets picture what is happening in the stock BOV when we let of the throttle with a fully pressurized system. The piston that is holding back boost has full boost pressure pushing back against it. The diaphragm has a hose connected to the intake manifold. The back side of the diaphragm has boost pressure on it trying to force the piston shut. Now, right before we let off the throttle, the top / intake side of the diaphragm has full boost pressure on it. The diaphragm has equalized pressure on both sides and it is solely the spring that is holding the BOV shut. As soon as the intake manifold creates vacuum, the top of the diaphragm will contain vacuum and the back side will have full boost. This will instantly open the valve up fully, and the system will vent. The back of the diaphragm will settle down to atmospheric pressure and the spring will force the valve close even if the intake manifold still has vacuum.
Ok, still with me?
Now with an aftermarket BOV, the back side of the diaphragm will have atmospheric pressure. So before we let off the throttle, the piston has full boost pushing on it, the top of the diaphragm has full boost holding it shut because the back side is atmospheric pressure and has less pressure than the intake manifold side. Note that a spring is not needed to hold the valve shut, as boost pressure vs atmospheric pressure will do this for you. As soon as you let off the throttle and the intake manifold builds vacuum, the top of the diaphragm will have vacuum and the backside of the diaphragm will still have atmospheric pressure. The vacuum will instantly open the valve and the system will vent. Spring pressure is required to keep the BOV shut during vacuum operation.
Make sense?
The BOV with atmospheric pressure reference will be able to hold much higher boost, because boost itself is holding the valve shut, where as the BOV with boost reference will require spring pressure to hold the valve shut. Spring pressure does not scale with boost.
The front side's reference is the intake manifold. So the back side needs a reference and we can choose from either atmospheric pressure like most all aftermarket BOV's have or we can choose to use boost pressure, which the stocker uses.
Lets picture what is happening in the stock BOV when we let of the throttle with a fully pressurized system. The piston that is holding back boost has full boost pressure pushing back against it. The diaphragm has a hose connected to the intake manifold. The back side of the diaphragm has boost pressure on it trying to force the piston shut. Now, right before we let off the throttle, the top / intake side of the diaphragm has full boost pressure on it. The diaphragm has equalized pressure on both sides and it is solely the spring that is holding the BOV shut. As soon as the intake manifold creates vacuum, the top of the diaphragm will contain vacuum and the back side will have full boost. This will instantly open the valve up fully, and the system will vent. The back of the diaphragm will settle down to atmospheric pressure and the spring will force the valve close even if the intake manifold still has vacuum.
Ok, still with me?
Now with an aftermarket BOV, the back side of the diaphragm will have atmospheric pressure. So before we let off the throttle, the piston has full boost pushing on it, the top of the diaphragm has full boost holding it shut because the back side is atmospheric pressure and has less pressure than the intake manifold side. Note that a spring is not needed to hold the valve shut, as boost pressure vs atmospheric pressure will do this for you. As soon as you let off the throttle and the intake manifold builds vacuum, the top of the diaphragm will have vacuum and the backside of the diaphragm will still have atmospheric pressure. The vacuum will instantly open the valve and the system will vent. Spring pressure is required to keep the BOV shut during vacuum operation.
Make sense?
The BOV with atmospheric pressure reference will be able to hold much higher boost, because boost itself is holding the valve shut, where as the BOV with boost reference will require spring pressure to hold the valve shut. Spring pressure does not scale with boost.
I think what you are trying to describe is a "flipped" blowoff where the input and output ports are switched.... but this does not necessarily apply to all aftermarket BOV. In fact, I think it only naturally applies to the synapse (although it can be done with any valve, including the stocker).
I think you are using alot of incorrect words in the wrong places to describe what is happening.
So, lets define:
BOV Input = Natural Pressure side (UICP on IX, LICP on X)
BOV Output = Natural Intake side or VTA
BOV Reference = The vacuum connection to the IM (which provides boost when the throttle is open)
I *think* you are trying to say that the stock configuration applies as above, and the BOV Input presses directly against the motion of the piston (IE, pushing it open, but for the action of the reference port). The reference and spring push on the other side and force the piston to stay closed when things are functioning properly.
I *think* you are trying to say that all aftermarket BOV apply as above, except the BOV input enters the valve perpendicular to the motion of the piston, whereby it naturally pushes the piston closed internally by trying to escape to the BOV Output (which means it pushes directly in-line with the closing motion of the piston as the air tries to escape). The reference and spring still push the valve closed (also directly in-line with the closing motion of the piston).
This last statement is incorrect though since, as I said, only the synapse is designed in such a manner. Other valves including the stocker can be run in this configuration, but it is not recommended.
No. All BOV's have some sort of actuator / diaphragm. This actuator has a shaft that comes out of it that controls the actual valve.
The Stock BOV has a port that runs up the back side of the physical BOV from the boost side of the BOV to the back side of the diaphragm. Take your stocker apart and look.
There are 4 things you need to define:
BOV Input = Natural Pressure side (UICP on IX, LICP on X)
BOV Output = Natural Intake side or VTA
BOV Reference A = The vacuum connection to the IM (which provides boost when the throttle is open)
BOV Reference B = The other side of the Actuator / Diaphragm that articulates the valve.
Here is a picture to illustrate what I am trying to say.
The Green Area is the part that I am talking about. It is what I have been referring to as "the back side of the diaphragm"
The Stock BOV has a port that runs up the back side of the physical BOV from the boost side of the BOV to the back side of the diaphragm. Take your stocker apart and look.
There are 4 things you need to define:
BOV Input = Natural Pressure side (UICP on IX, LICP on X)
BOV Output = Natural Intake side or VTA
BOV Reference A = The vacuum connection to the IM (which provides boost when the throttle is open)
BOV Reference B = The other side of the Actuator / Diaphragm that articulates the valve.
Here is a picture to illustrate what I am trying to say.
The Green Area is the part that I am talking about. It is what I have been referring to as "the back side of the diaphragm"
No. All BOV's have some sort of actuator / diaphragm. This actuator has a shaft that comes out of it that controls the actual valve.
The Stock BOV has a port that runs up the back side of the physical BOV from the boost side of the BOV to the back side of the diaphragm. Take your stocker apart and look.
There are 4 things you need to define:
BOV Input = Natural Pressure side (UICP on IX, LICP on X)
BOV Output = Natural Intake side or VTA
BOV Reference A = The vacuum connection to the IM (which provides boost when the throttle is open)
BOV Reference B = The other side of the Actuator / Diaphragm that articulates the valve.
Here is a picture to illustrate what I am trying to say.
The Green Area is the part that I am talking about. It is what I have been referring to as "the back side of the diaphragm"
The Stock BOV has a port that runs up the back side of the physical BOV from the boost side of the BOV to the back side of the diaphragm. Take your stocker apart and look.
There are 4 things you need to define:
BOV Input = Natural Pressure side (UICP on IX, LICP on X)
BOV Output = Natural Intake side or VTA
BOV Reference A = The vacuum connection to the IM (which provides boost when the throttle is open)
BOV Reference B = The other side of the Actuator / Diaphragm that articulates the valve.
Here is a picture to illustrate what I am trying to say.
The Green Area is the part that I am talking about. It is what I have been referring to as "the back side of the diaphragm"
I still disagree that all aftermarket BOV are open to atmosphere here though. The old Synapse had a port in your green/blue section to make it more "tunable", the new one has this internally referenced just like the stock BOV, the greddy type S has both connections to allow it to be "tunable", and other valves have both connections also.
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why you would ever want to electronically control the blowoff valve is beyond me, unless you were trying to build in additional overboost failsafes. car manufacturers have been doing this for years... my wife's 99 saab 9-3 viggen has a solenoid like this, as does the hyundai genesis coupe I believe.
You control a BOV electonically to develop in cabin precise, repeatable tunablity.
Therefore if your particular application required 0.8 second of FULLY OPEN BOV upon throttle lift to adequately vent the boost charge WITHOUT FLUTTER, you can tune it as such. You can also tune the BOV to respond with more or less sensitivity based on the rate of change of boost pressure seen in the manifold.
Thus you can have a snappier and more efficient BOV for a track run as compared to a detuned BOV for traffic/street conditions. It's all about optimising for your particular requirement at the touch of an in cabin button.
NOW the MOST IMPORTANT capability I am introducing is that of using the BOV as a low pressure wastegate for on throttle surge/flutter control.
Often the exhaust wastegate is pretensioned to 'hold' higher levels of boost. This pretension forms a floor under which the ebc cannot control boost. Should your application develop partial throttle compressor surge below that 'floor' you have no choice but to down size the turbo CFM. With BOV ebc, you can dial down the BOV spring tension to around 3 psi and thus achieve antisurge ebc down to that level.
Because the BOV is now driven by a map sensor feeding the controller & a WG solenoid via a small vacuum reservoir, it is not subject to false triggering.
Thus this new system permits larger turbos to be used in an application. The partial throttle surge happens because of varying Volumetric Eff. at different RPM. This is governed by manifold harmonics, cams, exhaust headers etc.
If your particular app. breathes better at WOT than at 50% throttle, this new system can allow you to take advantage of the extra CFM a larger turbo can deliver at WOT rather than downsizing the turbo to compensate for midthrottle flow limitations. Thus you will make more power at WOT, when u need it most.
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