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Performance Modifications for the NG900 / Old 9-3 This forum contains PERFORMANCE related Q&A's for the NG900 and 9-3. This may also include suspension.

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Old 09-03-2013, 08:29 PM   #1
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Viggen - Stg 3 - boost question

with stock turbo, but stag3 modifications (GS inlet pipe, 3" exhaust, race cat, etc)

If I start at a stop - and basically floor it, running through the gears - what should be the max PSI I see on a boost gauge?

Right now - I've got some work to do, (having ABS issues) but I have NO CEL
- I've cleaned the air filter, cleaned the MAF, done the bypass mod on the forge BPV, did the "bolt" mod (remove top vacuum from boost control valve - i'm going to just buy new 1 way valves - the bolt mod seems a bit ghetto for me), replaced the boost control valve, and am trying to tweak the right amount on the forge wastegate actuator (anyone know the right offset in mm from the wastegate pin to the hole in the turnbuckle)?

Reading from a bluetooth OBD reader to "Torque" on an android phone - the most I saw in my runs is 10.2 PSI. At idle - it sits at -9.6 PSI.

So - thoughts? If reading this from the OBD port is totally wrong, I get it - let me know. I'm just using what I have at the moment.

So - ideas? is this normal, or should I be looking for problems? If someone says "man, you should see 18 at least" - well, then I know I need to fix something...

No CEL is coming up when I push it hard.

help is appreciated. Thanks all!

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Old 09-04-2013, 06:45 AM   #2
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At idle it sits at 9.6 psi, do you mean vacuum, if so that is way low. Get a real boost gauge, those devices work somewhat, but they sample at to low of a rate.
ABS issue, did you disconnect it, if so you would be at BB? Do not tweek the wastagate rod, stages are set with BB usually set at stock or what the tuner states, make sure BB for your car is 6.5 and leave it, or does the forge only go as low as 8?

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Old 09-04-2013, 11:36 AM   #3
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Yes, vacuum. Usually that seems to be represented incorrectly as negative psi in some crappy equipment. So if this is low, what should vacuum be at at idle?


I'm not messing with the actuator to get performance, I'm trying to dial it in to where it should be.
Interesting what you say regarding the abs. Does this mean that as long as the car has abs problems it can't hit full boost?
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Old 09-04-2013, 12:17 PM   #4
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Quote:
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At idle it sits at 9.6 psi, do you mean vacuum, if so that is way low. Get a real boost gauge, those devices work somewhat, but they sample at to low of a rate.
ABS issue, did you disconnect it, if so you would be at BB? Do not tweek the wastagate rod, stages are set with BB usually set at stock or what the tuner states, make sure BB for your car is 6.5 and leave it, or does the forge only go as low as 8?
Every t7 car I've owned always was around 10 vacuum at cold idle and around 2o when warmed, a bit higher on deceleration 22-24. Never could figure out way so low once started cold even with replacing basically everything. All were around stage 2/3 hitting 18-20psi when wot
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Old 09-04-2013, 12:42 PM   #5
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I've explained this somewhere but can't find it.
Long story short is these cars run really retarded timing at idle and low manifold vacuum so the ECU can react very fast to changing idle loads (A/C, letting the clutch out) without the engine stalling by simply increasing the timing at a given amount of idle air to increase torque. The ECU can advance timing faster than It can command the IAC or TB open further and get that air to the cylinders to maintain idle speed.
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Old 09-04-2013, 03:33 PM   #6
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I've explained this somewhere but can't find it.
Long story short is these cars run really retarded timing at idle and low manifold vacuum so the ECU can react very fast to changing idle loads (A/C, letting the clutch out) without the engine stalling by simply increasing the timing at a given amount of idle air to increase torque. The ECU can advance timing faster than It can command the IAC or TB open further and get that air to the cylinders to maintain idle speed.
good info. Wisconsin! WOOT. I'm in Greenfield right outside Milwaukee.
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Old 09-05-2013, 03:22 AM   #7
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Every t7 car I've owned always was around 10 vacuum at cold idle and around 2o when warmed, a bit higher on deceleration 22-24. Never could figure out way so low once started cold even with replacing basically everything. All were around stage 2/3 hitting 18-20psi when wot
Same here, cold is way low, hot mine runs around 19. I was speculating that he was referring to hot idle?? I think the low cold vacuum is just to due to tolerances when cold, once things warm up and expand, vacuum goes up.
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Old 09-05-2013, 03:36 AM   #8
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Same here, cold is way low, hot mine runs around 19. I was speculating that he was referring to hot idle?? I think the low cold vacuum is just to due to tolerances when cold, once things warm up and expand, vacuum goes up.
Yes cold. Basically, start it, drive it, these are the numbers I'm seeing.. Sounds like until I can diagnose the abs issue I can't get a proper diagnosis on the boost. So am I only seeing base boost right now then? I would think 10 would be high for base?
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Old 09-05-2013, 07:13 AM   #9
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I just noticed you're running a forge wastegate actuator.
That is not a simple drop in replacement for the stock actuator. After modding the bpc and adjusting the pid map I finally got mine under control.
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Old 09-05-2013, 07:15 AM   #10
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As for the wastegate arm, about 2mm pretension there is pretty good. Adjust it to get to baseboost, 6-8psi about.

And the bolt mod, just try it at least to see if it helps. Could save you some money and effort.

And I'm always wiling to help out with another local Viggen!


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Old 09-05-2013, 07:17 AM   #11
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I just noticed you're running a forge wastegate actuator.
That is not a simple drop in replacement for the stock actuator. After modding the bpc and adjusting the pid map I finally got mine under control.

Good point on the forge WGA. What a PIA that was to get mapped right. His tune also probably isn't built for it. Response is quite a bit different than the stock WGA too.


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Old 09-05-2013, 09:43 AM   #12
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Good point on the forge WGA. What a PIA that was to get mapped right. His tune also probably isn't built for it. Response is quite a bit different than the stock WGA too.


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Indeed on the forge WGA. I've been messing with it a bit here and there, and trying to hone in on it. at first my mechanic (who is an expert, but NOT an expert on Saabs) put it in as a direct bolt in - and lined up the turnbuckle and put it on. I had...NO boost. and I was sad. So I read, and read...and read some more. talked with Joe (not sure his name on here, friend of mine owns, 5 saabs? black vig convert - oconomowoc). Joe said "that thing is a pain to adjust..." So I went out and shortened the WGA, so it was under tension. BOOM. boost was back. wasn't sure though if it was the right amount (as any amount was better than what I had). So now I'm just trying to tweak it. HOWEVER, it's hard to tweak this when everything else on the car is seemingly broken!

I do have a picture of the offset that I'm at right now though - I'll upload it if anyone is curious. Tell me if this is too much, enough, not enough...



So, in the process of all this, I was trying to diagnose a CEL as well as all the ABS lights being on. I got the CEL to go off (cleaned air filter, cleaned MAF, re-greased BPV, did bolt mod, and replaced the boost control valve in the front by the turbo inlet pipe) - cleared light. CEL has been off now for 80 miles even under driving at times like a maniac! WOO HOOO!. I also did the bypass mod for the BPV as well.

ABS - I sent in to be reman at BBA, got it back - ...sigh, no change. will check sensors on sat. (PS - I now have 1 extra ABS module, if anyone needs....)

So now - i am very low on boost (i should go to my neighbor with a measuring cup asking if I can borrow some PSI, as I'm all out of boost).

ran the Android app "Torque" today - vacuum at cold idle - 9.6 boost maximum hit today - 9.9

The question now is - can I diagnose the boost problem independently of the ABS problem, or are they linked somehow?

meanwhile, i'm blue silicone tubing things because I like the way it looks, and...i can, and I'm hoping it will eliminate leaks. the rubber hoses have NEVER been replaced and it's ...110,000 miles now. I do know that not everything can be silicone, so i'm being mindful of that.

Once I get all this banged out and the car is going like it should, and replace the plugs - I was going to call Brew City and get a new tune.... I think thats you Rabbit?!?
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Old 09-05-2013, 09:51 AM   #13
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Brew City Boost, ya that's me. Pretty sure we've met at at least one meet before. SlowJoe is Joes screen name here, he's a good ship!

Pretension looks like a good starting point. And Ido have lots of that blue silicone in stock too.

Gimme a call an we can talk about some plans. 261-352-9591


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Old 09-05-2013, 10:18 AM   #14
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Brew City Boost, ya that's me. Pretty sure we've met at at least one meet before. SlowJoe is Joes screen name here, he's a good ship!

Pretension looks like a good starting point. And Ido have lots of that blue silicone in stock too.

Gimme a call an we can talk about some plans. 261-352-9591


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how much silicone do I need, and what sizes? and what are your thoughts on this (photo attached) - cost isn't really an issue...:
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Old 09-05-2013, 11:27 AM   #15
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You should perform an actual base boost check. WIS has a procedure, or just bypass the bpc and connect the compressor outlet port to the wg actuator and go for a drive.
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Old 09-05-2013, 11:35 AM   #16
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The problem with the forge actuator is not only is the base boost a lot higher (10-11lbs) with no preload, the valve takes a bit more pressure to get it to swing open fast. Coupled with a quick spooling td04 it loves to overshoot untamed.
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Old 09-05-2013, 11:41 AM   #17
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Once you unplug the abs on a T7 it goes into base boost, once you plug it back in, non-base boost. OK, so if you have a viggen, stock BB is set at 6.5. Now go down to your local car part store and pick up a cheap ass psi gauge that reads vacuum as well and T into it, run line through window and check BB. Since you have a stage 3 there really is not any reason to go beyond 6.5. My car is a stage 5, was mapped on the road at 6.5 and I have increased BB to 7.5 and higher, and it ran worse at the top end, so back to 6.5 I went. Once set at 6.5, car warm, you should see no less than 16 in vacuum, if less then you have a leak. At sea level my stage 3 viggen with 91 oct ran 11.5 max boost. So run the right plugs, the right gas, replace all the vacuum lines, get gauge, test and report back. Until then, throw darts.
OR,stop, bring to brew city and have them sort it out.
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Old 09-05-2013, 11:53 AM   #18
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Once you unplug the abs on a T7 it goes into base boost, once you plug it back in, non-base boost. OK, so if you have a viggen, stock BB is set at 6.5. Now go down to your local car part store and pick up a cheap ass psi gauge that reads vacuum as well and T into it, run line through window and check BB. Since you have a stage 3 there really is not any reason to go beyond 6.5. My car is a stage 5, was mapped on the road at 6.5 and I have increased BB to 7.5 and higher, and it ran worse at the top end, so back to 6.5 I went. Once set at 6.5, car warm, you should see no less than 16 in vacuum, if less then you have a leak. At sea level my stage 3 viggen with 91 oct ran 11.5 max boost. So run the right plugs, the right gas, replace all the vacuum lines, get gauge, test and report back. Until then, throw darts.
OR,stop, bring to brew city and have them sort it out.
Absolutely outstanding how to info. Very helpful. Thank you!!
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Old 09-05-2013, 03:22 PM   #19
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If you have open SID (you should if you have a fairly modern tune), look at your real boost there, you don't need an additional gauge. Connect the compressor outlet line that goes to the BPC directly to the wg actuator, bring up the manifold pressure reading on the SID, and go for a drive. Then you know your base boost and you've spent no money.

The stock spring in the Forge unit will put you around 8psi when things are right. That's a good target for something in the stage 3 range if the boost control in your tune is worth anything. (needing to run helper springs, and things like 15 psi base boost at a stage 3 level means there's something wrong)

If you're above 8psi then you want to make the actuator arm longer by threading it out further. 1 full turn will be worth somewhere around .5 psi
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Last edited by Drew in Houston; 09-05-2013 at 03:24 PM.
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Old 09-05-2013, 04:17 PM   #20
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If you have open SID (you should if you have a fairly modern tune), look at your real boost there, you don't need an additional gauge. Connect the compressor outlet line that goes to the BPC directly to the wg actuator, bring up the manifold pressure reading on the SID, and go for a drive. Then you know your base boost and you've spent no money.

The stock spring in the Forge unit will put you around 8psi when things are right. That's a good target for something in the stage 3 range if the boost control in your tune is worth anything. (needing to run helper springs, and things like 15 psi base boost at a stage 3 level means there's something wrong)

If you're above 8psi then you want to make the actuator arm longer by threading it out further. 1 full turn will be worth somewhere around .5 psi

Tune is from maptun via Genuine saab in 2011.

good info. Stock spring in my actuator is "green" - that's what they sent with it, I think there is 1 softer than that? I believe I got some of my research from your site. The info I found out there was 1 turn of the turnbuckle on the stock actuator rod was .29 PSI or .02 bar (genuine saab gives .02 bar and I just converted it). The forge is more than that? If so, that explains why I'm seeing a base boost right now (due to the ABS being out) of highest value 8.9 PSI on my gizmo (photo attached of high/low and Idle). - sounds like I need to go 2 turns "longer" and I'll be where I need to be to at least start moving forward.

This thing is reading from the OBD port via bluetooth. handy, but I question how accurate it is (though it has matched on other readings perfectly...)

It's really quite nice when things start making sense, and activities actually show improvement, it makes me love my car again.
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