WG: Regulates pressure on the exhaust side i.e turbo boost
BOV: Regulates pressure on the intake side. Stops excessive flow back pressure on the turbo vanes after the throttle plate close
That's all correct, but I'll add one more thing. The BOV (AKA Diverter valve) provides a secondary safety function, the ECU can command it open anytime it's wants to lower boost if it doesn't see what it wants from manipulating the wastegate.
As far as i know, This limit is controlled by the waste gate , which "sees" the intake pressure and opens up when the limit is reached to vent off or bypass the exhaust gas around the turbo (vented to the catalytic converter or atmosphere), thus preventing it from spinning faster and creating more boost. It doesn't vent out the intake air.
That's mostly correct, but just off enough to cause of confusion. The wastegate doesn't exactly see the intake pressure. It sees whatever the ECU decides it gets to see, which is never above intake pressure, but could be a lot lower.
Hence , the waste gate controls the maximum boost pressure (limited by how much your engine can take/ turbo rev limit etc).
Changing how much your waste gate "sees" can allow you to increase this limit (increase maximum boost)
What you are saying would have been 100% correct not that long ago, but it's not really accurate with the 4C. If you change the boost signal to the wastegate without allowing it to go through the ECU it will cause huge problems. As soon as the ECU notices that it's not able to control boost by manipulating the wastegate via the boost solenoid, it's going to end the fun by closing the throttle and opening the diverter valve.
A blow off valve, on the other hand, lies on the intake side and is meant to open up when the throttle is closed (by sensing engine vacuum). This vents out the pressurized intake air to the atmosphere. This is required because as you rev the engine up , the turbo spools up as well. The instant the throttle is let go, the turbo continues to create boost which now has no where to go. This causes the turbo to quickly spool down which creates a lot of impulsive stress on the turbo. Consequently , the turbo (now having spooled down) will take time to spool up when the throttle is re-applied.
Hence the blow-off valve protects your turbo by allow it to continue to spin (rotational inertia) and vent out the un-required air, when the throttle is closed. A consequence of which is reduced turbo lag eg. between gear shifts etc. Installing high flow blow off valves may improve turbo spool performance to a perceivable extent.
The stock diverter works pretty well in this application. The turbo doesn't loose much speed during upshifts due to the fast shifting of the TCT and the ECU's manipulation of the throttle and diverter valve. An upgraded valve might be better, but it just hasn't been a problem yet. There are two potential advantages, faster pressure drop, and cooler air charge as a result of not putting hot boosted air back through the turbo for a second trip through the compressor. I am just not sure how much of advantage there would be in practical terms.
Poor bov design chirping
like when the throttle closes during a shift. When a BOV is vented to atmosphere, it produces a distinctive hissing sound, and when a BOV isnít used or is of insufficient size, the compressor surges and makes a chirping or rattling sound. Compressor surge can put stress on the compressor and its bearings, shortening its life. I hear this chirpping all the time, meaning the oem blow off valve, being plastic is not that good...i.e plastic
Let's remember that Borg Warner, who made the turbo is the one who decided that this valve is the right size for the turbo. We certainly don't see turbos failing in the 4C, so regardless of what you think you hear, I just don't think there is a problem. I am NOT saying that what you hear isn't relevant, and I am NOT saying that there are not improvements to be made, but I don't think it's too important with the current flow requirements.
For cars with metered air (a flapper valve or hot wire MAF sensor), it is best to route the vented air back into the pipe between the MAF sensor and the turbo to avoid a moment of rich mixture caused by the missing air.
The 4C does have such a sensor, but unlike older cars, this valve is electronically controlled. I am not so sure that bypassing to the atmosphere would cause a problem because the ECU knows when it's open and when it's open the engine is in a falling condition anyway. This is nothing like the older cars where the valve was open any time the engine was off boost and thus mixture would be totally thrown off in most driving conditions if you bypassed to the atmosphere. Then again, I haven't done it on the 4C, so I can't say with absolute certainty.
For a car that does not have an air flow meter, you can just vent the air to the atmosphere with no ill effects on the mixture.
No question about that.
So any point in afternarket actuator, or at least bov, or adaptor plate ,, at least for sound and or reliability?
I just don't think it's worth doing at THIS point in time. Now with some of the future developments, maybe.