even at idle the turbo will be spooled enough to eliminate the manifold vacuum,
Don't take this the wrong way.
But you really don't know much about how a motor works do you???
A motor canot run without vacuum.
At idle any car, and the 335 runs at about 18 inch of vacuum.
Thats more then enogh to open the valve.
The car will always run under vacuum until you creat enough load to build boost.
See this video i did back in December.
Notice the vacuum my car has will driving.
Then I push in the clutch and rev it out to hear the HKS BOV.
0 boost is at the 11:30 positin on the gauge. And 20 inch of vacuum at 9:00.
Just go pop the hood on you 335, undo the return tube from the diverter valve and see for yourself instead of saying thing you don't know.