john s

<center><img src="http://thebench.laer.nu/strips/tt-50-0.jpg"></center><p>Here is one (courtesy Robert Bosch GmgH*) for the fuel pressure regulator, general principle the same. As you can see, in the closed position, the area of the diaphragm seen by port #6 is much greater than that of port #7. The same spring & vacuum levels will give different results depending on flow orientation. For boost on port #6, when the valve opens there is a small increase in area and an associated drop in pressure as boost vents to #7. The area within the seat of #7 can be made to minimize the change in force as the valve opens. However if #7 is the boost side, then as the valve opens, a much larger area is exposed and the valve swings wide open as soon as it begins to leak. This might be tolerable in the spooldown application but in overboost protection & economizer mode this would cause noticeable engine torque variations. I am surprised switching the plumbing on the OEM valve doesn’t cause a more noticeable difference. Really need to take one apart. Too bad the people selling other DV’s don’t offer specifications for the valve they’re replacing or supplying.

* for illustrative purposes only

Marius

Brilliant, Steve, thanks! I'm surprised as well, reversal ought to show in diagnostic data...

Marius

Sorry, John, I apologize for that one. Now I AM an Audi apologist! ;-)

Marius

Yes, there IS a very large difference in areas presented to (6) and (7), and if our OEM valves are anything like this it's incomprehendable to me that a valve reversal should not prevent satisfactory functionality, or go unnoticed through design and production test procedures. Mounting it the wrong way would also completely disable any overboost protection independant of intake vacuum control.

Still there's the possibility that the DV valve is very different from this. The mystery goes on...