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Discussion Starter #1
So this is the forge valve from genuine saab I am going to order for my '08 big T.

http://www.genuinesaab.com/catalog/product_info.php?products_id=873&osCsid=

I just wanted to have someone verify that this is correct since it specifies '03-'07.

Secondly, where do you find the spring kit to hold higher boost once tuned? I plan to have it tuned, either JZW or BCB is what I am thinking, after doing a clutch and exhaust, maybe stage 3 eventually, which I would need injectors and IC for I believe. It would just be nice to have the spring kit on hand rather than having to get it once I have the tune. I just didn't see it anywhere on the genuine saab site, do I need to go directly to Forge?
 

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It fits. I installed one on my 2008 with a JZW Stage 1 aggressive tune. But it caused a BPC circuit MIL and put me in limp home. That was because I stupidly used the medium "yellow" spring instead of the softest ("green") one. I sold it and re-installed the stock BPV.
If you really want and need the yellow spring, you can order the BPV and the yellow spring at Viva Performance. Wish I could remember where I bought mine, it came with 3 different springs with the BPV.
 

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Discussion Starter #3
Did it come with the alternate (stiffer) springs? I read that the springs were sold separately. Why did you get rid of it instead of putting in the softer spring?
 

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Did it come with the alternate (stiffer) springs? I read that the springs were sold separately. Why did you get rid of it instead of putting in the softer spring?
See my edited post about the springs.

I was tired of messing with it so I bailed. I probably should have kept it and tried the softest spring, but that is supposedly the same as having a stock valve anyway. And if it did not work and I kept getting the CEL, I would have had to remove it again and then install the stock valve anyway. And it was cold outside. And the sun was in my eyes. And, and . . . so I bailed.
 

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Okay, I went out to the car and found the receipt.
I bought mine from Viva Perfromance - SKU# VP-031105, same as on their website. For some reason, mine came with the green, yellow and red springs.
 

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Discussion Starter #6
Haha, understandable, that sun will get ya. Yes, from what I read the softest spring mimics the factory valve, I think I am getting blow by though, so the machined piston rather than a leaky diaphragm and the ability to modify for higher boost is the benefit. Thanks for the info, I am going to order it tonight. I will just order the spring kit when the need arises.
 

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Haha, understandable, that sun will get ya. Yes, from what I read the softest spring mimics the factory valve, I think I am getting blow by though, so the machined piston rather than a leaky diaphragm and the ability to modify for higher boost is the benefit. Thanks for the info, I am going to order it tonight. I will just order the spring kit when the need arises.
Talk to John at JZW first. I bought mine thinking the squealing/screaming sound I was hearing after the tune was blow through on the diaphragm. Changing in the Forge valve did not get rid of the squealing/screaming. I talked to John about it and he said T8 decidedly does not play nice with these valves. He promised me that putting back the stock valve would eliminate the code and the limp home problem and he was right. He also stated the stock valve was more than adequate for the Stage 1 aggressive tune. And it has been thus far, since September of 2012.
 

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Discussion Starter #8
Ok, I have sent a message to Taliaferro to find out how to acquire the spring kit, and I'm sure I won't hear from them until tomorrow. I don't have a tune, YET!! At least to the best of my knowledge, I bought my 9-3 about 3 months ago and it wasn't specified, not that that would've been specified. This is the first saab I have owned but I don't think it feels tuned. Thanks again for the input.
 

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JZW is a fan of the stock ones over the Forge units. They work just fine and are spec'd to our cars exactly. Boost flutter is normal, that is T8 doing it's job.
 

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Discussion Starter #10
I understand that T8 will regulate how much boost is being applied, but it seems like it takes more time to get into boost at WOT now than when I first bought it. Also, as I don't have any experience with saabs until now, with the windows down there is quite a lot of "whoosh" while in boost, this leads me to believe that there is significant blow by, or a good hole in a rubber hose somewhere (need to check for this if "whoosh" isn't normal). T8 doesn't control the BPV I wouldn't think, just the spring inside and vacuum line to the back side of the diaphragm has been my experience with blow-offs? Does this signify blow by on the seal to any of you with more experience with these systems? Its not like I can create load at a stand still to check for it under the hood, it also doesn't seem to pull as hard as it did initially which means either I have gotten used to it, or something has degraded, or T8 has adjusted due to some variable. Without having the experience with these cars I can't really pinpoint so if anyone has some insight it is appreciated.
 

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I understand that T8 will regulate how much boost is being applied, but it seems like it takes more time to get into boost at WOT now than when I first bought it. Also, as I don't have any experience with saabs until now, with the windows down there is quite a lot of "whoosh" while in boost, this leads me to believe that there is significant blow by, or a good hole in a rubber hose somewhere (need to check for this if "whoosh" isn't normal). T8 doesn't control the BPV I wouldn't think, just the spring inside and vacuum line to the back side of the diaphragm has been my experience with blow-offs? Does this signify blow by on the seal to any of you with more experience with these systems? Its not like I can create load at a stand still to check for it under the hood, it also doesn't seem to pull as hard as it did initially which means either I have gotten used to it, or something has degraded, or T8 has adjusted due to some variable. Without having the experience with these cars I can't really pinpoint so if anyone has some insight it is appreciated.
Turn the car off and pull the F2 fuse in the fuse block in the engine bay. Immediately replace the fuse and then start your car and go for a drive. Then tell us how it drives after that.
 

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I understand that T8 will regulate how much boost is being applied, but it seems like it takes more time to get into boost at WOT now than when I first bought it. Also, as I don't have any experience with saabs until now, with the windows down there is quite a lot of "whoosh" while in boost, this leads me to believe that there is significant blow by, or a good hole in a rubber hose somewhere (need to check for this if "whoosh" isn't normal). T8 doesn't control the BPV I wouldn't think, just the spring inside and vacuum line to the back side of the diaphragm has been my experience with blow-offs? Does this signify blow by on the seal to any of you with more experience with these systems? Its not like I can create load at a stand still to check for it under the hood, it also doesn't seem to pull as hard as it did initially which means either I have gotten used to it, or something has degraded, or T8 has adjusted due to some variable. Without having the experience with these cars I can't really pinpoint so if anyone has some insight it is appreciated.
I went directly from T5 to T8 and my experience with by-pass/blow off valves was as you described it - the ECU used the BPC and the waste gate to control boost. The BPV only came into play to vent excess pressure in the intake tract in off-throttle mode to prevent compressor stress/stall. T8 is much more active than T5 which was a speed density/boost request system. No IAC so it uses the throttle plate to regulate air intake from idle to WOT. It measures and monitors many more engine parameters than T5 and must account at all time for the air mass measured initially by the MAF. It operates primarily as as a torque request system and is governed tightly by the MAF readings. From my discussions with John I learned that the BPV is used in conjunction with the waste gate to control the boost that is generated for the most part to meet the torque request from the ECU maps which are determined in conjunction with the MAF and pedal position sensor readings (and of course modified by the knock and/or misfire count experienced in under-load dynamic situations).

This was quite eye-opening for me. I was firmly convinced as you are that the BPV existed as a more or less passive-reactive secondary system with a single limited function (as previously described). But John insisted that the BPV has evolved into a much more active adjunct boost control and assured me that excessive clamping was resulting in short-term over boosting that triggered the limp home mode. He told me if I re-installed the stock valve the issue would disappear and he was RIGHT. And it all made sense to me after that. I just had to unlearn what I thought I knew (or more accurately, realize its inapplicability to the newer engine management system).
 

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Discussion Starter #13
Interesting, thanks Saaboheme for the update and explanation. It makes sense when you think about it as being a more efficient and accurate method to control boost with both the wastegate and BPV. These ECUs are something of a wonder, and make the task of learning them that much more intriguing and satisfying.

I was doing a brake job this weekend and had a 3/8" drive E20, needless to say, it has to be a 1/2" drive. I twisted off two 1/2"-3/8" adapters (1 being impact grade) so now I am waiting for the E20 1/2" drive impact socket I ordered, so I haven't pulled the F2 fuse. As soon as I get the brakes done I will try pulling the fuse.
 

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So this is the forge valve from genuine saab I am going to order for my '08 big T.

http://www.genuinesaab.com/catalog/product_info.php?products_id=873&osCsid=

I just wanted to have someone verify that this is correct since it specifies '03-'07.

Secondly, where do you find the spring kit to hold higher boost once tuned? I plan to have it tuned, either JZW or BCB is what I am thinking, after doing a clutch and exhaust, maybe stage 3 eventually, which I would need injectors and IC for I believe. It would just be nice to have the spring kit on hand rather than having to get it once I have the tune. I just didn't see it anywhere on the genuine saab site, do I need to go directly to Forge?
I have it installed on my Saab 93 2.0T. I also have JZW stage 3 tune. The one I ordered from Genuine Saab only came with 1 spring. I have not had any error codes or any other issues. The turbo will still make a squeal noise when at high boost. I think at lower boost the Genuine Saab one stays closed better so you can build boost quicker. It also could be my imagination.

The stock one is a POS. It almost feels like it's made out of tinfoil.
 

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So hold on. My flutter with my stage 1 tune is normal? I am letting out precious boost though and would like to keep it in. 2006 93 2.0T. Are you guys saying that my car will go into limp mode installing the forge BPV?

Also, Saabohème, you should have tried the shims to fine tune between the green and yellow springs. Put in the green (same as stock) and add a shim to make it hold a bit more psi, but less than yellow.
 

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So hold on. My flutter with my stage 1 tune is normal? I am letting out precious boost though and would like to keep it in. 2006 93 2.0T. Are you guys saying that my car will go into limp mode installing the forge BPV?

Also, Saabohème, you should have tried the shims to fine tune between the green and yellow springs. Put in the green (same as stock) and add a shim to make it hold a bit more psi, but less than yellow.
I am getting older, maybe not wiser. But definitely older. And the old back does not take to bending over the engine bay like it used to. So experimenting, in November, outside, in the rain and cold, was simply not on the agenda. Plus, I had no shims. Could have used large washers I suppose, but again, once I knew the Forge did not eliminate the screaming and John highly recommended returning to the stock valve, I said "frack it" I am putting the stock valve back in. And I got about 80% of my moolah back by selling the Forge.

If you dial the Forge in like you have described you should not get a code or limp home. But by doing that, the Forge will not hold more boost than T8 requires to meet a given torque request. So you will not be holding in significantly more boost than the stock valve is holding.

I suspect that T8 is walking a very thin tightrope compared to T5 and T7. With T5 the bypass valve acted solely as a means to vent excess pressure from the high pressure side when the throttle plate closed to save wear and tear on the compressor wheel, and open throttle boost pressure itself was regulated solely via the BPC and waste gate. With T8 it seems the ECU needs to vent some high pressure side boost pressure to help it very quickly adjust the boost pressure. There is some small delay using the waste gate only before pressure in the high pressure portion of the intake tract drops (i.e. the post-turbo part of the intake tract), so it does make some sense to use the bypass valve in conjunction with the waste gate to keep boost pressure where the ECU wants it, especially if the T8 ECU demands tighter control of the boost pressure than T5 or T7 did.
 

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Now that I watched these videos, I understand what you are saying. I had no idea what a bpv was or how it worked. :)

https://www.youtube.com/watch?v=5g6cHs5vMRE

Now that I understand to some extent how this works, it raises more questions.

Is the BPV controlled by the ECU or is it controlled by the green spring? The youtube video shows the spring reacts to the pressure and then the ecu reacts to the spring to open the valve. Get a hard enough spring and the ecu will delay opening the valve, and we don't lose our boost. Correct?

Also, if getting tuned, would one not want to change the wastegate/actuator to an adjustable one? I would assume raising the psi by tuning would cause the WG to open pre-maturely.

I am running an MPS tune from stopsign on this site

Wategate: For people like me, here's the vid.
https://www.youtube.com/watch?v=vGhlgphrBxA (skip to 3:07)

Pardon my ignorance but I'm reading/learning
 

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Now that I watched these videos, I understand what you are saying. I had no idea what a bpv was or how it worked. :)

https://www.youtube.com/watch?v=5g6cHs5vMRE

Now that I understand to some extent how this works, it raises more questions.

Is the BPV controlled by the ECU or is it controlled by the green spring? The youtube video shows the spring reacts to the pressure and then the ecu reacts to the spring to open the valve. Get a hard enough spring and the ecu will delay opening the valve, and we don't lose our boost. Correct?

Also, if getting tuned, would one not want to change the wastegate/actuator to an adjustable one? I would assume raising the psi by tuning would cause the WG to open pre-maturely.

I am running an MPS tune from stopsign on this site

Wategate: For people like me, here's the vid.
https://www.youtube.com/watch?v=vGhlgphrBxA (skip to 3:07)

Pardon my ignorance but I'm reading/learning
IIRC, with T5 and T7 the valve is purely mechanically controlled by vacuum. The spring is there to help the valve resist opening that would otherwise occur as a result of the positive pressure in the intake tract. At open throttle, the vac line also has positive pressure inside it to help keep the valve closed. When the throttle plate closes, during braking and/or shifting, the positive pressure in the vacuum line becomes negative or vacuum. At this time the positive pressure building up in the intake tract becomes enough to force the valve open (since there is vacuum on the other side of it now). If the spring is way too strong, the valve will not open at all or not enough, and excess pressure will remain inside the intake tract and possibly stall the compressor wheel.

I am guessing here, but with T8, I suspect that one of the solenoid valves used (most likely the one mounted near the throttle body rather than the one on the turbo which is nearest the waste gate), may operate to help modulate the vacuum seen by the bypass valve. In T5 and T7 there is only the one boost pressure control valve or solenoid to regulate airflow and vacuum and it controls the waste gate operation. With a second solenoid valve, the T8 ECU can thus tell that BPC solenoid to close partially or all the way to create full or partial vacuum at the bypass valve, at partial or full throttle (instead of having vacuum only occur when the throttle plate closes), to help regulate boost.

So, unlike T5 and T7 which utilize the bypass valve solely as an excess pressure vent for the purpose of preventing compressor stall or stress, the T8 system can utilize it in conjunction with the waste gate to get faster and more precise control over the boost pressure itself.

A theoretical discussion of active control of boost pressure and torque using the bypass valve.
 

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IIRC, with T5 and T7 the valve is purely mechanically controlled by vacuum. The spring is there to help the valve resist opening that would otherwise occur as a result of the positive pressure in the intake tract. At open throttle, the vac line also has positive pressure inside it to help keep the valve closed. When the throttle plate closes, during braking and/or shifting, the positive pressure in the vacuum line becomes negative or vacuum. At this time the positive pressure building up in the intake tract becomes enough to force the valve open (since there is vacuum on the other side of it now). If the spring is way too strong, the valve will not open at all or not enough, and excess pressure will remain inside the intake tract and possibly stall the compressor wheel.

I am guessing here, but with T8, I suspect that one of the solenoid valves used (most likely the one mounted near the throttle body rather than the one on the turbo which is nearest the waste gate), may operate to help modulate the vacuum seen by the bypass valve. In T5 and T7 there is only the one boost pressure control valve or solenoid to regulate airflow and vacuum and it controls the waste gate operation. With a second solenoid valve, the T8 ECU can thus tell that BPC solenoid to close partially or all the way to create full or partial vacuum at the bypass valve, at partial or full throttle (instead of having vacuum only occur when the throttle plate closes), to help regulate boost.

So, unlike T5 and T7 which utilize the bypass valve solely as an excess pressure vent for the purpose of preventing compressor stall or stress, the T8 system can utilize it in conjunction with the waste gate to get faster and more precise control over the boost pressure itself.

A theoretical discussion of active control of boost pressure and torque using the bypass valve.
seek and you will find:

I knew there was a reason why the diaphragm only works with the T8!

I kept thinking the ECU has parameters to control the Solenoid which controls the opening on the diaphragm, so the compressor can divert back to the intake track. This PDF is a eye opener.

Thanks Saaboheme
 
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