Originally Posted by Biggiesacks

thinking about it some more, the surface area of the valve vs the size of the hose going to the diaphragm housing are pretty unequal. So the valve would see the initial pressure spike before the diaphragm could build enough pressure to push back against it causing the valve to blow open and vent the pressure, thus the spring is needed to help prevent that from happening.

Originally Posted by letsgetthisdone

Tial does talk about this, and they to not use less than a 6psi spring in the Q bov unless its a supercharged app because a squick spooling turbo could cause the valve to open before the diaphragm sees enough pressure from the reference line to stay shut. But, that would only occur during spoolup. On a slower spooling turbo, a light spring will still hold all the boost.

Originally Posted by 2006EvoIXer

There should never be a vacuum between throttlebody and intercooler (including the "bottom side") because turbo intake can't suck it into a vacuum without the DV closing and cutting it off.

Originally Posted by 2006EvoIXer

How much are you boosting?

Originally Posted by Biggiesacks

Well at least I was in the right ballpark. Someday someone will probably come up with an electronic solution, kind of like an MBC vs a 3port BCS. At this point its probably more trouble then its worth, that is until it isn't.

Originally Posted by 2006EvoIXer

Let me try to explain what I understand and hopefully don't confuse you more.

The top side of diaphragm is connected to intake manifold between throttlebody and valves. When off throttle, it sees a vacuum from pistons sucking and throttlebody being closed.
The bottom side of diaphragm will only see boost because it is plumbed to the pressurized piping between throttlebody and intercooler (same as air we are recirculating with DV). When DV opens from vacuum at top of diaphragm or enough pressure from bottom of diaphragm over coming the spring and top diaphragm pressure, it opens and purges the pressure (recirculating to turbo intake). Onced purged, the bottom of diaphragm sees the same reduced pressure as what's in the pipe between throttlebody and intercooler. You are correct that the bottom side of diaphragm is slightly delayed because of the pathway from source pressure. I think (my opinion) this gives us the nice midrange boost spike before bleeding off the boost in the higher RPMs.

There should never be a vacuum between throttlebody and intercooler (including the "bottom side") because turbo intake can't suck it into a vacuum without the DV closing and cutting it off.

Originally Posted by kaj

26psi, but not the problem.
If my DV has a faulty diaphragm, maybe that's why I seem to have a leak, but can't find it during a test. I wouldn't think to check there...and that's IF I would even hear it.

Originally Posted by kaj

26psi, but not the problem.
If my DV has a faulty diaphragm, maybe that's why I seem to have a leak, but can't find it during a test. I wouldn't think to check there...and that's IF I would even hear it.

Originally Posted by Biggiesacks

The bottom side of the diaphragm is exposed to the outlet of the DV, in a recirculating system that would be going into the intake, which does see vacuum all the time the engine is running. I think you are mistaking the bottom side of the diaphragm for the actual valve that closes against the pressurized pipe.

Originally Posted by 2006EvoIXer

The bottom of diaphragm is connected to the intake side of DV through the hole on the side connected to pipe between throttlebody and intercooler.

Originally Posted by 2006EvoIXer

If your diaphram was leaking, it wouldn't open at 26-27 psi. I think it should hold more pressure before opening since the bottom of diaphragm will have less pressure from leaking into intake manifold.

Take off you DV and pull a vacuum on top diaphragm (nipple). If vacuum goes away, then it's leaking.