I just purchased a Forge diverter valve, also known as a bypass valve, for my SAAB 9-5 as a birthday present to myself. My stock Bosh DV was obviously weakened, but the diaphragm had not deteriorated to the point of hooting. I ordered the FMCL007P Forge DV and spring set from Amazon.com for $135 plus $13 S&H.
I was surprised by how big it was compared to the stock Bosh DV. The extra bulk is mainly in the screw-off top. I installed the green spring and inserted none of the spacers.
Forge lists the springs as:
Green – 5-15 PSI
Yellow – 15-23 PSI
Blue – 23-30 PSI
Spacers are used to nudge the spring tension. The LPT 9-5 would use green or green with spacers. I would encourage people to try both the green, green with spacers and yellow springs and see what they discover for themselves. I have read of Aero owners using the yellow spring with spacers.I have no input to give about the blue spring because I don’t want to try it out in my SAAB. I know it is too strong for my LTP and I don’t want to damage anything.
This wasn’t even a five minute job. Opening the hood took longer than this installation. I used a pair of pliers to release the two tension collars that hold the stock bypass valve in place. The valve comes out with some wiggling. Carefully remove the vacuum hose on top with your fingers or with a very light touch of the pliers if it is stuck.
Then install the new Forge bypass valve by reversing the steps. I guess you might leave the vacuum hose for last when you install. Some people post about the vacuum hose being too tight to go on the new diverter valve. The advice given to them is to heat the little hose in a glass of hot water to make it more pliable. I didn’t have any problems installing the vacuum hose on mine.
You can see how much more it sticks out compared to the Bosh bypass valve. Plenty of clearance on the 9-5, so this isn’t an issue.
My stock diaphragm style Bosh DV was weakening and didn’t consistently hold or release pressure. The Forge DV has increase the feeling of performance, but obviously just replacing the failing DV has made a difference. I leave it at this because don’t have a turbo pressure gauge or dyno to confirm my feelings with hard numbers. The T7 recognizes when the turbo pressure is too great and responds by lowering performance, and I have no idea if there is a gray area of increased turbo pressure; where there is more boost than stock, but not so much that the computer fights it. One SAABCentral poster described a 1-2psi increase after adding the Forge with a yellow spring. The pressure being read from his after market gauge. But like I said, I don’t have any instruments to read the pressure or performance and the SAAB 9-5 likes to foil bolt-on performance parts.
There is also a difference in sound. The Forge has what I would call a three syllable sound. My Bosh only had two syllables when it released. The Bosh was a K-Shhh sound and the Forge is more of a K-tik-Shh sound. It doesn’t sound is any louder, it is more that it now sounds like a “BOV” instead of a random air leak; same volume, more distinct sound.
More information about Forge and Bosh diverter valves.
“The great diverter valve face-off”
The SAAB 9-5 uses a diverter valve (DV) or bypass valve in place of a blow off valve (BOV). The casual term “hooter valve” is sometimes used because of the sound it makes. The DV functions like a BOV, but it recirculates the released air back into the air intake instead of releasing it into the atmosphere. I haven’t tried it, but I understand that letting the SAAB 9-5 release pressure into the air will be read by the T7 as a vacuum leak and the car will go into limp mode with a CEL.
Getting a performance diverted valve, like the one made by Forge, and installing it in the reverse configuration will further enhance the sound of the turbo.