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Discussion Starter #1
This mod it so that you can bypass the vacuum valve that is mounted to the firewall that controls the bypass valve. The vacuum valve keeps the valve from releasing suddenly at low pressure, so to keep the car more "subtle" for the daily driver. This mod will make the bypass run on true pressure of the system. The control is not actually needed, but should remain plugged in so that the t7 system thinks it is still functioning.

Materials

2 to 3 feet of correct size vacuum hose (may not be needed)
1 vacuum nipple cap of same inner diameter.

Step 1

Follow the hose from the bypass valve to the firewall and you will see where it is connected to the control valve. (In my picture the control is not connected to the firewall due to it being new, yours should be located underneath the big red plug assembly)
http://www.saabcentral.com/forums/attachment.php?attachmentid=22257&stc=1&d=1301073610
http://www.saabcentral.com/forums/attachment.php?attachmentid=22258&stc=1&d=1301073900

Step 2

Once you have found the valve, follow the two other hoses leading out of it.
One should lead to the throttle body, and the other to the air manifold (the one to the manifold may have a t inline somewhere).
http://www.saabcentral.com/forums/attachment.php?attachmentid=22259&stc=1&d=1301073989
http://www.saabcentral.com/forums/attachment.php?attachmentid=22260&stc=1&d=1301073989

Step 3
Remove the line completely that runs from the throttle body to the control, and cap the nipple on the thottle body.
http://www.saabcentral.com/forums/attachment.php?attachmentid=22261&stc=1&d=1301074069

Step 4
Remove the line from the manifold to the control completely (If there is a t remove it only after the t).

Step 5
Remove the old line from the bypass to the control and run the new vacuum line directly to the nipple on the manifold (or t if applicable).
(note: The old line may be long enough to cover this distance)

You're all finished.
Now your bypass will run on true manifold pressure, not electronically limited pressure.
 

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This mod it so that you can bypass the vacuum valve that is mounted to the firewall that controls the bypass valve. The vacuum valve keeps the valve from releasing suddenly at low pressure, so to keep the car more "subtle" for the daily driver. This mod will make the bypass run on true pressure of the system. The control is not actually needed, but should remain plugged in so that the t7 system thinks it is still functioning.

Materials

2 to 3 feet of correct size vacuum hose (may not be needed)
1 vacuum nipple cap of same inner diameter.

Step 1

Follow the hose from the bypass valve to the firewall and you will see where it is connected to the control valve. (In my picture the control is not connected to the firewall due to it being new, yours should be located underneath the big red plug assembly)
http://www.saabcentral.com/forums/attachment.php?attachmentid=22257&stc=1&d=1301073610
http://www.saabcentral.com/forums/attachment.php?attachmentid=22258&stc=1&d=1301073900

Step 2

Once you have found the valve, follow the two other hoses leading out of it.
One should lead to the throttle body, and the other to the air manifold (the one to the manifold may have a t inline somewhere).
http://www.saabcentral.com/forums/attachment.php?attachmentid=22259&stc=1&d=1301073989
http://www.saabcentral.com/forums/attachment.php?attachmentid=22260&stc=1&d=1301073989

Step 3
Remove the line completely that runs from the throttle body to the control, and cap the nipple on the thottle body.
http://www.saabcentral.com/forums/attachment.php?attachmentid=22261&stc=1&d=1301074069

Step 4
Remove the line from the manifold to the control completely (If there is a t remove it only after the t).

Step 5
Remove the old line from the bypass to the control and run the new vacuum line directly to the nipple on the manifold (or t if applicable).
(note: The old line may be long enough to cover this distance)

You're all finished.
Now your bypass will run on true manifold pressure, not electronically limited pressure.
Thanks for the info. So on a scale of 1-10 how would you rate the difference over the original setup?
 

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Out of curiosity, do you know if the stock valve is meant to see vacuum? I ask because on a previous car of mine I ran a line straight from the intake manifold to the valve and the valve would make a humming sound in vacuum (idle, etc). After some research I learned that the valve I was using is made to handle boost pressure, but not vacuum, which is why the valve was vibrating and making the noise.

Does that make sense?

I wonder if the stock setup has a check valve in it which prevents the bypass valve from seeing vacuum.
 

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Discussion Starter #4
Well the info i originally got this from is from taliaferro so i'd assume he knew what he was talking about. I haven't gotten any humming so far today. Now as for difference in performance or anything, nothing really. It did get mostly rid of the hooting in my valve though. It seems that the control was letting the valve release just enough to hoot and now that it is pretty much all open or all closed the hooting is actually a challenge to recreate.
 

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Discussion Starter #5
Out of curiosity, do you know if the stock valve is meant to see vacuum? I ask because on a previous car of mine I ran a line straight from the intake manifold to the valve and the valve would make a humming sound in vacuum (idle, etc). After some research I learned that the valve I was using is made to handle boost pressure, but not vacuum, which is why the valve was vibrating and making the noise.

Does that make sense?

I wonder if the stock setup has a check valve in it which prevents the bypass valve from seeing vacuum.
Just curious as well. How is a bypass not supposed to see vacuum. Is it spring loaded and just goes to the original setting when the boost is removed?
It just seems like vacuum is needed to really release the pressure effectively.
 

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Hmm. . . can the unaltered intake manifold pressure actuate the valve properly? If attached directly to the intake manifold an overboost condition should clamp the valve shut. Please feel free to correct my logic as I am no engine or turbo expert.
 

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can the unaltered intake manifold pressure actuate the valve properly? If attached directly to the intake manifold an overboost condition should clamp the valve shut.
Sure, overboost will hold the bypass valve shut. Bypass valve ONLY actuates on a lift-throttle condition when you suddenly have a vacuum in the intake manifold; then the valve opens to allow the compressed air downstream of the turbo to recirculate to the upstream side of the turbo. It prevents sudden buildup of pressure between the turbo and a closed throttle plate.
 

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Discussion Starter #9
It shouldn't clamp it shut. It would just stay shut as always. Overboost should just be the system keeping the wastegate from opening until a higher pressure. As for the bypass it shouldn't be any different.
 

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Overboost should just be the system keeping the wastegate from opening until a higher pressure.
I have an auto-box, so no built in overboost. Maybe this could give me a little more grunt for cheap/free. (or at least more turbo sound)
This mod seems like it would work, I may try it when I get my car back from the shop. (cursed ABS module)
 

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Discussion Starter #11
Well after reading up on this mod from other sources it seems the biggest advantage is supposed to be a quicker valve response due to the lack of the delay from the control valve
 

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Just tried this mod out on my car. Still too soon to draw any conclusions on the performance aspect, but my initial gut feeling is positive. I also appear to have fixed a tiny vacuum leak in the process, as the connections to the solenoid were barely holding on, and I have a slightly higher vacuum reading at idle, which could also contribute to a performance difference.

Basically all you need to do this are a vacuum cap, and a 2-way barbed vacuum line connector. Put the cap on the throttle body vacuum outlet as described in the first post, and remove that hose completely. The other two remaining hoses that connect to the solenoid can just be connected together with the vacuum line joiner. Shouldn't need to replace any hose that way! I was lucky and had a vacuum T installed for my boost gauge already, so I just hooked up to that.

Would only suggest bothering with this mod if you have an aftermarket piston style bypass valve like a Forge or Hyperboost, otherwise the valve will "hoot" and could fail prematurely.

In addition to this mod, if you have a piston valve you may also want to consider running your valve "backwards" to the stock orientation, with the piston pointing towards the delivery pipe. If you do this, keep in mind you need to adjust the spring tension so the piston isn't pushed open by the boost. This means with a Forge valve you need the yellow spring at least, or with the Hyperboost Adjustibles you crank down the preload screw by about 50% or so. You need a boost gauge to verify that you are still achieving the same boost levels as before, so that there is no leaking from the piston. With the above mod, the boost pressure will also be pushing on the back side of the bypass valve, helping the spring to hold it shut, so you would need less preload than if you ran without the vacuum line mod as well.
 

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Just tried this mod out on my car. Still too soon to draw any conclusions on the performance aspect, but my initial gut feeling is positive. I also appear to have fixed a tiny vacuum leak in the process, as the connections to the solenoid were barely holding on, and I have a slightly higher vacuum reading at idle, which could also contribute to a performance difference.

Basically all you need to do this are a vacuum cap, and a 2-way barbed vacuum line connector. Put the cap on the throttle body vacuum outlet as described in the first post, and remove that hose completely. The other two remaining hoses that connect to the solenoid can just be connected together with the vacuum line joiner. Shouldn't need to replace any hose that way! I was lucky and had a vacuum T installed for my boost gauge already, so I just hooked up to that.

Would only suggest bothering with this mod if you have an aftermarket piston style bypass valve like a Forge or Hyperboost, otherwise the valve will "hoot" and could fail prematurely.

In addition to this mod, if you have a piston valve you may also want to consider running your valve "backwards" to the stock orientation, with the piston pointing towards the delivery pipe. If you do this, keep in mind you need to adjust the spring tension so the piston isn't pushed open by the boost. This means with a Forge valve you need the yellow spring at least, or with the Hyperboost Adjustibles you crank down the preload screw by about 50% or so. You need a boost gauge to verify that you are still achieving the same boost levels as before, so that there is no leaking from the piston. With the above mod, the boost pressure will also be pushing on the back side of the bypass valve, helping the spring to hold it shut, so you would need less preload than if you ran without the vacuum line mod as well.
If we do this and keep the orientation as regular with the piston valve, we're still good, right?
 

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Just did this today, first person I passed turned their head to look, even at 35 mph, the difference is noticeable. Now just to wait on my cold air intake, piston dump valve, and larger delivery pipe and I should be golden.
 

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Just knocked this mod out last night. Nice. Little bit more response to the throttle, takes about 10 min to do, and costs a few $ for the parts.
 

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Instead of running through the control that is linked to the ECU, it instead runs the diverter valve (bypass) off of pure manifold pressure. It gives you a bit more response to the throttle as it reacts to pressure instead of a computer.
 

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Instead of running through the control that is linked to the ECU, it instead runs the diverter valve (bypass) off of pure manifold pressure. It gives you a bit more response to the throttle as it reacts to pressure instead of a computer.
ohh i see okay the DIY confuses me ahaha but il try and figure it out.
 

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ohh i see okay the DIY confuses me ahaha but il try and figure it out.
It's not as difficult as it seems. Follow the vacuum hose from the bypass to the firewall, that is the control unit. There is one hose from the control unit that goes to the throttle, the other goes to a "t" (that goes to the manifold). Remove the hose from the throttle to the control unit and make sure you cap the nipple tight at the throttle (don't want any extra air going in). Then remove the hose from the "t" to the control unit. Take the original hose from the bypass off of the control unit and connect it to the "t". Done.
 
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