diagnosticator1

gauge, falling, as the throttle closes, and close again when the manifold pressure equals zero gauge transitioning from vacuum to positive boost pressure. In addition the ideal DV would open and close in a snap action, being either closed tight, or open 100 percent.

In order that the DV open as close to zero manifold pressure as possible the lightest spring that overcomes the friction of the internals, is used. As the spring gets stiffer, the delay increases between the zero pressure transition point and the actual manifold pressure when the DV opens, the delay, causing some boost air flow to stall at the throttle valve reducing turbo speed. For example, if a light spring provided a DV opening pressure of 2 in Hg vacuum pressure, and a stiffer spring required 10 in Hg vacuum pressure in the manifold before opening, the boost air flow will stall at the throttle during the delay. When this happens, the turbo slows down, and the boost pressure recovery after the gear shift, is delayed even more.

More to follow.....

diagnosticator1

Nothing posted by Mike@Forge contradicts my description on why the DV orientation is correct (IE, "reversed" compared to the OEM orientation,) with the inlet port at the center bottom and the discharge at the side port. The explanations posted by Mike@Forge, are consistent with and confirm the reasoning I employed by my attempt to describe the operational aspects involved.
It's necessary to limit the scope of discussion to recirculating setups, as used on our Audis. Other setups like atmospheric venting, etc and the different operational aspects of the pressure relief valves used, are irrelevant in the context of recirculating boost pressure relief valves.
The pics are provided by Mike@Forge, I copied the URLs from his posting on the Evo Forum:

<img src="http://www.hostdub.com/albums/MikeForge_album04/bov_closed.gif">
<img src="http://www.hostdub.com/albums/MikeForge_album04/bov_open.gif">

In the pics, the flow direction is "Reversed from OEM" or the correct direction as I tried to explain.

I am unclear on your comments stating that the application of boost at the side port, and also at the control port, will hold the valve closed, because in that case, there is no pressure differential forces on the piston/diaphragm, other than the spring force and the small pressure force created be the different effective areas of the two sides of the piston/diaphragm, holding the valve closed. (Spring side of diaphragm, Force = area * pressure, On the other or bottom side of the piston/diaphragm, Force = [Total area - area of inlet port cross section] * pressure) The net effective force holding the valve closed, using vector sign, where + = up and - = down, Total Closing force = -[force on top side of piston/diaphragm] + [Force on bottom side of piston/diaphragm = -[Net closing force] or Net force downwards holding the piston/diaphragm on the inlet port seat, NOT including the -spring force.

To be sure, it's a complicated system to visualize, it takes a while to synthesize a complete understanding of the dynamics of the valve as effected by the installed orientation in the system, and on the charge air pressure/manifold pressure relationship to throttle valve angle.

More to follow later...

diagnosticator1

any relevant information for comparative uses, and in practical terms,is a useless waste of time and effort, and only confuses the issues.
Whether the DV holds X pressure or not, without control pressure/vacuum also applied at the control port consistent with control pressures as installed, or worse, with the port capped, is meaningless and is not representative of the capability existing as installed.

modwad

I was running "reverse of OE" with blue spring and both shims. Valve made really loud whistle upon pressure dump that I grew to love.
Currently, I'm running in "same as OE" or the "as directed by forge" position with blue spring and no shims.
Car seems smoother on boost and achieves full boost faster according to gauge vs. RPM. It is also much quieter with no whistle.
I haven't logged yet as it's been raining and I don't want to travel to my log site if it's going to rain.
If you read the AZ post, Pat from Forge explains the pressure in the side port a little better.
I would bet that a different spring is needed for the "same as OE" than the "reverse of OE" position. My guess would be a less-stiff spring for the "same as OE" position since boost isn't directly applied to the direction of piston travel. But I could be wrong. I'd kind of like to know though.
I do want to switch back to "reverse of OE" position, but more due to sound than function. I swear the car just runs better in the "same as OE" position that I've switched it to, but that could be due to removing shims and maybe has nothing to do with position.

diagnosticator1

He felt the response was definitely worse than the Bailey piston DV he had be used to. When he tried the R1 in the reversed from OE position, he reported the car was much more responsive.
The physics involved with a piston DV and a diaphragm DV are very similar, especially regarding Forge DVs and OE. But the dynamics of a piston type DV do vary somewhat compared to a diaphragm type valve. In particular, the DV opening response vs the closing speed can be optimized for either aspect of the DVs operation, but not both at the same time.

I remember hearing that when the TT225 was first on the market, there where some issues with the DV noise that many complained about. So Audi began installing the DV reversed to address the noise complaints.

The results you obtained by the recently changed DV setup, are at best, speculation concerning what the swapped flow direction and it's effects on the difference in DV behavior you noticed, because more than one variable was changed at the same time.

For sure, DV dynamics and the relationship with engine behavior, is one of the most difficult concepts to understand thoroughly and correctly. Only a few people really have a good grasp of the situation, even the experts disagree, thus the conflicting information often encountered. For example, the situation as explained by different guys at Forge, in response to your inquiry, and in reply to forum questions posted before by others.

I should have emphasized that my perspective on the hows and whys explaining the "correct is reversed from OEM orientation" is derived from the facts of DIAPHRAGM DV dynamics, I have not used piston DVs myself, and have never examined the subtle differences that piston DV properties have as related to dynamic behavior. Although in general, the main concepts comparing the two types of DV operational principles are very similar. In consideration of the technical facts relevant to the subject, and lacking any opposing theory/s that can withstand careful technical scrutiny, I am confident that my explanation and justifications supporting my position, are technically correct.

modwad

And APR claims install in any position other than "same as OE" voids warranty

Room4TU

uhhhh, what the hell did you just say?