That's because you have a surge ported compressor cover . I run the red spring in my DV too w/ a ported cover, I get no part throttle flutter or surge. Holds boost like nothing else.

 

I tried reversing my valve and still have the fluttering problem at part throttle in the middle RPM ranges. If I'm at ~3500 rpm and push the throttle about 60-70% I'll start to build boost and then the car starts bucking as boost builds. I have the yellow spring in as that is the softest spring I have. I may try returning it to the stock position and a slightly lighter spring than I had before. Anyone have any suggestions or could you let me know which spring and shim combination is working for you? I was running the yellow spring without shims in the reverse orientation and the yellow spring with 2 shims in the normal orientation. Both held boost and both fluttered some.

-Paul

 

bringing this back from the grave, anyone find a reliable fix for this? Tried reversing orientation with no luck...what springs are people who have this working right using?

 

Sorry to bring this back up, but here are my recent findings.

I reversed my Forge RS a few days ago due to part-throttle flutter problems for the past year. I have noticed a few things.

1. Part throttle low boost will not cause the valve to lift, I believe because the valve is already being opened by engine vacuum and the turbo charger flow rate is low enough that the pressure never builds up in the IC piping. The air simply flows out before it builds up, preventing the PSSHH sound.

2. Improved fuel econ. This may be my imagination, but with most of my driving on the interstate in > 15" vacuum the valve is open due to the spring being backed all the way off. This allows air to flow around the turbo reducing any flow restrictions in the intake path while in vacuum.

3. Part throttle fluttering is gone. Driveability!

4. WOT sound has changed from a fluttery series of reliefs (my spring was too tight, but to hold 27 psi, I had to use almost max spring pressure) to a single relief.

My only concern with this configuration is the posibility of compressor stress. When the throttle plate shuts, the pressure climbs in the IC piping, forcing the valve to seat harder. This is contradictory to post #8, but working with valves and marine mechanical systems for a long time, I don't see how raising pressure on the upstream body-side of a seated valve will cause it to lift. Maybe the beveled radial cut along the valve piston (disc), but I would have to research before accepting that idea. When engine vacuum finally is strong enough to pull the valve open, all the remaining air is relieved. I have not noticed any delay in the time to relief and the time that the throttle is closed, so I believe that the compressor is not under any extra stress or expeirencing any surge effects.