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Blow Off Valve (BOV)/Diverter Valve (DV) Install - Audi A4

Prior Experience: None
Cost: approx. $5
Time: 45 minutes

Discuss this mod - Here

I landed a sick deal on a GFB Stealth FX valve for the car, so I decided to give it a shot. I was previously running the Forge 007 but was aching for the Blow Off Valve sound. After cancelling an order for a Forge 004, I found this GFB Stealth FX. For those who dont already know, this valve give you the option to adjust how much of the bossted air is recirculated and how much is blown off. The valve has a dial with 16 'clicks' of adjustment. All the way in one direction an dthe valve functions as a full BOV, all the way in the other and it functions as a full DV. For our cars is supposedy bad to run a full BOV, so with this valve I can run 75% BOV and 25% DV or any other combination I can think of. Here are some pics:

Audi A4 BOV   Audi A4 BOV
Full DV      Full BOV

SUPPLIES - Since I was replacing a 007, I didn't need any supplies other than the valve. If this is the first valve install you do, then you will need 3 new hose clamps as the ones on there are one time use only. NOTE: those one time use clamps SUCK to get off!


Since my car is dumped, I can't get up on ramps or jacks without removing my kit. So I took off my front bumper and headlights which helped a bit with this install. Presumabley, you don't have to do this, and you shouldnt do it just to do the valve - its not needed.

The first thing you have to do is to remove the plastic cover on the underside of the car. To do this, just get the car up on ramps. You'll need a flathead screwdriver to dis-engage the 6 screws arond the edges of the plastic cover (only a 1/2 turn each gets them out)

  Audi A4 BOV
With the cover removed you can see where the valve is located (you can also see this from above if you know where to look)
Audi A4 BOV  

Audi A4 BOV

From Above      From Below

The valve has three hoses going to it.

1) The thin one is the vaccuum hose.
2) The one that is pointing straight up out of the hood of the car is the boosted line.
3) After the valve opens, air is recirculated through the remaining hose

Note: In the pics above, the Forge 007 is installed in "Reverse". Because of this, you will see can see the vacuum line on top

Audi A4 BOV

The GFB Stealth and the GFB Hybrid are both designed to be installed this way - Vaccum line up. So it is a direct replacement for the valve I have installed. IF YOU HAVE A STOCK VALVE you will have to make sure you remember to "reverse" the new valve if necessary.

After I disconnected all the hoses and swapped out the valve, I just had put that cover back on and I was done.

If you happen to have the Stealth FX, some additional "tuning" is needed.

The procedure can be found here on the GFB Site

  Audi A4 BOV
Audi A4 BOV    

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