To start, a little history.
I got the valve sometime ago and it had the old style piston. When installed like stock, it makes a squeak/screech noise that is both loud and annoying. The other orientation it is fine. I got a new style piston from Forge and installed that with a blue spring.

Now today for the hell of it I decided to put the cone filter back on the car. What I found is the valve makes a flutter type noise when it opens. I tried different springs and they were no help. Another member on here ported his valve to enlarge the opening and managed to eliminate this flutter noise. What I believe from hearing this noise, is it is not actual flutter but the sound of the air trying to escape the valve (larger piston, less air space) and buffeting over the ribs designed in the piston. I am convinced the valve is opening and not actually fluttering. I then proceeded to install the original piston with the blue spring. Install in stock orientation is still makes the noise, so for now I have it backwards, so to speak.

Conclusion to all this is, first the new style valves are not actually fluttering. They open properly, just the design of the piston is causing an odd noise. This helps explain why everyone is putting in the green spring and still have the noise. There is just not enough cfm of flow with that piston. The porting of the valve body helped eleviate the problem.

Second, the old piston allows much more airflow when it opens. The downside is the noise. What I believe is the problem in the proper orientation is the side port (turbo side) is a pressed in fitting. It seems that the quality air flow this piston provides generates enough velocity to cause a whistle (for lack of a better term) when the valve opens and the air passes across the edge of the side port. The indentation in the face of this valve or the seat do not seen to be able to cause such a noise. I smoothed the edges of the piston and seat and it has no effect on the noise. I have not changed the side port in anyway as I do not have good porting tools on hand.

Forge, if you would like to discuss this I can call you. I spoke to you previously on the phone for about 15 minutes when I got the new piston. I am happy to work with you on these issues if you want to try out some test pieces. Either the side port needs to be blended to the valve and the original piston can be used. Or the new piston needs to be slimed down (remove the fluting) so the valve can flow more air but still maintain a decent seat area. The advantage to the new piston is the increased capacity of the vacuum area helps up the valves opening point. The old piston is smaller and takes less initial engine vacuum to put the piston under vacuum. The old piston design with a blue spring easily holds 22 psi (peak) on my car. Since it has better flow characterisitic, I think it be better if the side port was blended or if I am wrong the noise screech noise is resolved.
This is clearly a great valve by design, but I would prefer to run it like the stock orientation. Right now I have it the other way, which works but that doesn't put the boost pressure on the face, which is ultimately better.

 

Bump.

 

.......

 

Forge please respond what are the the correct sequence of the color of the spring ie softest to stiffest

 

Actually the valve is fluttering. I had bad experiences with this valve on the racecourse. Mid corner mild releasing of the throttle caused nasty back and forth chassis movement. In other words the engine just stumbles in an on/off motion. Full release of the throttle is ok at best. Im very unhappy with this valve but im not planning on spending any more money. I spoke with Forge but got no true answers to a fix for this problem. On a roadcourse this fluttering can be very dangerous because of the unsteady weight transfers.

 

What spring are you running in there? I have the Yellow installed (stock boost, etc), and it seems to perform quite well. I might try the Green since I've heard that will hold the stock boost, and since it's a slightly less stiff spring, it should open more on partial throttle...

 

I tried all the springs. The green spring still flutters and also leaks boost. I tried blue, yellow, same ****z. I may go with a 1g bov, not sure yet.

 

instead of posting to a public forum where they might not happen to read it, instead why not call forge or email them?

forgeusa@fdn.com

 

Achtuning's really taking off huh? I bought a bunch of ko4 conversion parts off of Josh when he first started the company. Before he had any advertising or anything. He's a cool guy. I had a laser red S4 also a 00. Miss the luxo factor, but not the cost of modifications. The evo is a beast. To each his own.

 

yeah man, it's been really fun! I actually started the company with Josh...I'm enjoying it. The evo is a beast, why do you think I'm getting one for myself, heh.

Josh will keep his S4 though, and we'll probably get a new V8 S4 as well.

 

I emailed them about this post when I posted it, they said they would read it and get back to me.

 

cool, I actually just ordered a few of those from forge for our shop, be nice to see what their resolution to this is.

 

Josh is going to be PO'ed when you spank him at half the cost. I love the new S4 though. Any ideas for the motor yet?