Currently rebuilding one of my project car, changing the body (Canada rust) and many parts.

Years ago I planned to run two HKS valves on a single turbo set-up. One before the intercooler that would vent to atmosphere and one after the intercooler that would recirculate. And switch which one is operational using a manual 3 way ball valve to control which one the vacuum signal goes to.

The car I am rebuilding ran a single vent to atmosphere BOV, it runs 94 octane and got an average millage of 10 mpg. With the price of gas I have changed the build and decided to run EGR again but also decided I am going to install the BOV/BPV set up on this car.
The car runs a Vane Air Flow Meter so all air vented to atmosphere is metered air and the fuel to match it burns off in the exhaust.

My question is, despite the fact these BOV's are on the charge pipe which isn't considered a vacuum source is there any chance of them opening between shifts without a signal going to the vacuum port. I know they will stay closed under boost but before I purchase and weld two HKS flanges to to piping I would like some thoughts on the matter.

I know your probably thinking I should just run the BPV and give up on the childish sound of the BOV, but I have 3 HKS SSQ's and bough a fancy insert for one years ago, and I have ran BOV's on everyone of my cars. 90% of the time they serve no purpose except making noise and wasting fuel but they (especially the HKS) are very good at moving dormant drivers out of the left lane.

Other fuel saving efforts:
-Using the widebands simulated, programmable narrow band auxiliary connection to control the ECU which operated open loop after 3000 rpm, to run leaner A/F's below 3000rpm.
-I swapped the Simple Digital System Extra Injector Controllers on board 2.5 bar map sensor for a 2.5 bar Gauge Pressure Sensor (0-36psi control).
-Running 91 Octane fuel and having water/methanol injection come on at 18 psi boost instead of at 21psi boost.
-Switching from a factory front mount intecooler with 2.5" pipes welded to it, to a larger aftermarket front mount intercooler, yes cooler air is more dense and requires more fuel to maintain exhaust A/F ratios but these cars run rich and use extra fuel to cool charge air, (11.8-11.3 A/F's under boost). The car runs an intake air sensor and gauge so I am hoping to be able to lean it out a bit based on IAT's, while matching current EGT's.
-MSD boost timing retard with 2 bar map sensor swapped for 2 bar gauge sensor (0-30psi) to pull a bit of factory timing at higher boosts to allow for 91 octane.
-Might even have some lead removed from my right foot.

 

Nothing wrong with a little BOV noise. They will very likely be cracked open at idle, and letting some unmetered air out. Is the Air metering before the turbos (meaning passes through the meter on the way to the turbo)?

 

Thank you for the reply.

Yes the air meter is before the turbo, I have tried running it after the turbo and BOV but every time the blow off valve would open and close (super sequential) the vane air flow meter would slap shut, it sounded like the 3 stooges where raping a turkey under the hood and the air flow meter box isn't strong enough to handle the pressure, one fast spool bent the lower aluminum cover and popped the black cap of the top causing huge vacuum leaks.

Not because I am stubborn and want to hear a different answer but because I want to rationalize this think to death before attempting or giving up the idea. This gives me the opportunity to explain and or correct my rationalizing of these BOV's operation.

My though (correct me if I'm wrong) is if with Vacuum signal from the manifold drawing 20in/hg on the BOV signal port and the ventury effect of moving air causing vacuum or suction on the HKS valves inside the BOV the spring still keeps the valve shut at idle. Shutting off the signal port hose and locking it in an atmosphere pressure state, wouldn't there be less draw on the valves inside the BOV.
I plan to try using a shop vac on hks valve to see if it will suck the valve opened with nothing hooked up to the signal port.

I feel as though these valves are completely operated by the boost vacuum signal port and have nothing to do with the pressures inside the charge pipe, small twists of the throttle pulley with the engine idling in neutral will open the BOV.
But all in depth descriptions of the pull style BOV mention differential pressure between the valves and the spring chamber cause it to open, I believe if the HKS valve is held in your hand and the signal port is connected to a N/A engines vacuum signal the valve would open to dropping engine vacuum after revving the engine or is this wrong?

Do the HKS valves preload the spring to open the valve when they are pushed on by boost pressure?

I did think it would be important to only operate the 3way ball valve with the engine off to keep atmosphere pressure in the shut BOV signal passage, switching them under vacuum at idle could aid in causing the shut valve to open. Switching them under boost and trying to keep the signal line pressurized is impractical.

Back when the extra BOV and inserts where purchased this hole design was based on the fact that when I installed my first HKS SSQ BOV I got the vacuum line for the factory BPV and the one going to the air filter box mixed up, when testing with the hood opened manually turning the throttle the only thing that would happen was the Air flow meter door would slam shut due to turbo pressure buildup before it, sounded like a turkey the guys that where with me said it sounded cool, I said it's not working at all and switched the vacuum lines.
Reflecting on the installation and planing it out again 15+ years latter, I can only think that tells me nothing about what happens when driving the car and large volumes of air are in constant state change.
Back then I would have said this idea will work based on my accidental under the hood R&D with HKS SSQ BOV's and an engine in neutral. Today I join a forum and ask, it only takes one overlooked detail or fact and the best design and planning fail.