Interesting... So in your experience:
- The leaking at idle/cruise does not impact mileage.
- Spooling has improved with your authentic SSQV versus the knockoff. Presumably the authentic unit vents better than the knockoff.
And, how do you know how my BOV sounds? Is this Craig?
If so I'll reserve my SSQV questions until later.
Another interesting note. I looked into the Synapse BOV from these guys:
It is a pull design like the HKS, but uses a piston instead of a diaphragm. Based on the youtube videos It looks like their valve stays open at idle and maybe at part cruise, and only shuts under boost. Based on some things I read that the Synapse designer/engineer/whoever posted in their forum it has something they call economy mode. And, if you add this little spring/piston device that prevents leaking at idle (for the MAF crowd), the economy mode does not work. So, reading between the lines, I think maybe they are indirectly claiming increased efficiency based on a cruise load BOV leak.
Soo... this ties into an alternate theory I have on efficiency. What if having the BOV open slightly at cruise is a GOOD thing? Think of it this way... The throttle, at a given cruise speed and load (say flat terrain) is ultimately determining the manifold vacuum. If pressure upstream of the throttle is increased (by a non-leaking BOV) then manifold vacuum is decreased, and the throttle closes further to compensate, returning the manifold to the steady-state vacuum required for the given cruise speed and load. This would not help the throttling loss, but would actually increase it. Plus the turbo is working harder since the flow rate is the same but the compressor outlet is at a higher pressure (upstream of the throttle). This equates to more restriction on the turbine side since it is also working harder, feeding power to the compressor.
So let's say that the BOV is allowed to leak a bit at cruise speed at the same given load. The post-compressor/pre-throttle pressure drops, so now at a given flow rate the compressor is not working as hard since the pressure rise is reduced. There is also a corresponding drop in turbine restriction. And, the throttle is open farther since there is less pressure upstream and it can open up farther for the target steady-state manifold vacuum. NOTE: The given flow rate assumption may not be true here, because the leak in the BOV means there is more flow across the compressor than just what the engine is ingesting. Whether it is significant flow through the BOV compared to the engine I do not know.
So, if I am not way off here, it may actually be beneficial to cruise mileage to have a slightly leaky BOV. I am assuming here that it is not a huge leak that would allow the turbo to overspool. And the BOV would immediately seal up when the throttle was opened up to produce more power (boost). The most efficient point of this transition from slightly leaky to sealed could be tricky. To be clear, I am talking about small leaks at cruise due to the position of the BOV, and not due to a bad seal.