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Garage Queen Club
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Discussion Starter #1 (Edited)
Been trying to figure this out for some time:

- 6768 w/Antisurge housing and quick spool valve
- One SSQV BOV before fmic, one after, both plumbed to port on intake manifold
- Car boosts clean, even at low rpm. No compessor surge noted
- Boost leaked system, no leaks noticed

When attempting to hold 5-10psi for the entire rev range, I get a fluttering issue which seems to come from the blow off valve. It becomes unbearable when trying hold partial throttle/power through a turn on the road coarse.

There are no adjustments on these new HKS SSQV. It seems that when at partial boost, but throttle at about 60%, violent fluttering occurs and I have to let off, and get back on it. Basically, I can only cruise or run full throttle.

Anyone experience this before? Is it probable that at 5 psi measured at the intake manifold, there could be 6, 7 or a bit more before the FMIC (obviously if there is pressure drop), causing that BOV to begin fluttering due to slightly less boost on the back of the BOV valve?

This link explains what I'm seeing:

EDIT: Doing more research...

Seems this is an ongoing issue for many folks, for quite a few years. Here is my theory and a potential way to fix this.
1. You are at 30% throttle, 4000rpm, trying to maintain half boost (say 10psi). Manifold pressure (post throttle body TB) and pre-TB are 10psi, BOV closed. All good.
2. You are now at 5000rpm, exhaust energy wants to spin turbo more, starts creating more boost, say 14psi. You let off TB to 10% to keep 10psi. Now you have an issue: BOV sees a pressure differential of 4psi, and it does what it is supposed to do - vents the air until it equalizes back to 10psi.
3. BOV closed again, all good. Now you are at 5500rpm, and the cycle happens again. Now you get the flutter occurring during part throttle.

Wonder if I were to connect a MAC solenoid valve to the vacuum port on the BOV. Port1: Manifold vacuum, Port2: to BOV, Port3: open air (always 0 psi), and have AEM control it as such:
1. When boost is below ~5psi, BOV -> Manifold vacuum - works as normal
2. When boost is between 5psi and some upper mid range (say 15psi), AND throttle is between 0% and 50%, BOV -> Open air: This will cause the BOV to open and release pressure indefinitely, but only so much that you may be able to maintain a certain lower level of boost. How much I don't know...
3. When boost is 15psi+, AND throttle >50%, BOV -> Manifold vacuum - works as normal

This mapping may need to be 3D: Load, throttle and RPM based.

Another option for 2. is to connect the 3rd MAC port to a pre-TB boost source instead of open air. This will force the BOV to remain closed in part throttle (no pressure differential). But, if you now have ~14psi pre-TB, and 10psi post-TB (with TB at 10%), you may induce compressor surge... or maybe not.
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