Had a thought today, I think it could be useful....
I can't count the number of people that call in ask if something is wrong when their BOV opens under vacuum at idle.
Nothing is really WRONG per say, if it has enough spring to stay closed @ idle with 18-20" of vacuum then its not going to blow off till there is at LEAST 9-10psi of difference between the bottom BOV and top port of the BOV. Its ALOT more than that most of the time considering most BOVs have a larger actuator to valve surface area ratio.
Here is my idea- It requires a dual port (lift and close) BOV like our 60mm JGS600. Take a pre-throttle reference line thru a regulator and plug it into the lift port. Set the regulator (on a bench feeding with another regulator set @ peak boost PSI) for less than it takes to LIFT the bov (no counter pressure in the BOV close port). Basically whatever a light BOV spring opens at is what your trying to mimic. If the light BOV opens at 4-5psi on the lift side and the heavy spring opens at 10psi and you'll want the regulator set to give 4psi.

This will mimic a lighter spring when the turbo is making boost and keep the BOV shut under engine vacuum. The regulator will only apply X amount of pressure so its only countering the excessive spring pressure.

Feel free to punch holes in my theory, it was a MONDAY

 

It will work as you stated.

Tom Vaught

 

Thanks Tom, only down side is a lack of letting the compressor free spin at idle?

 

It will still be doing work only not against a severe restriction.

The only way that you really need to worry would be if you put the INLET side of the Turbo in a vacuum (with the engine still supplying exhaust energy) which would be the same thing as doing a Burst Test on a Hot Stand. Compressor blade has no resistance and the turbine blade has lots of energy so you get a massive over-speed. Even then, on Burst tests, the turbo is typically modded with a "flaw" to create the Burst condition.

"Free Spin" at idle will not be a problem, as the compressor is still doing some work.

Tom Vaught

 

Burst test sounds wicked LOL.
Too much pressure to the bov "lift" port and it'll bleed boost... not in a good way.
Its definitely one of the more cost effective vent-only methods.
$15-$20 regulator + tees and hoses.

 

So far this is working well on my test car. We set the pressure to the bottom port to allow the bov to open with 8" vacuum using a 25" vacuum spring pack. This is the extreme end as that's the heaviest springs I have. But all is working well so far.

 

Old thread I know, but any more info? Perhaps a diagram of what you did?

 

The top/main bov port is hooked up to the intake manifold like normal.
The secondary port (that is able to open the valve with pressure) gets hooked to pressure pre-throttle body via a small regulator.
Bench set method
Using springs that will fully resist engine idle vacuum I hook compressed air (set to boost pressure levels) to the regulator.
Then attach a vacuum pump to the top port to the top port and pump up say 8".
Finally add air with the regulator till the valve barely moves.

In theory a 25" spring would need ~ 8.5 psi to make a ~4.5 psi (factoring in the valve face vs. actuator size of our 60mm BOV) opening differential pressure which good for thrust bearings.