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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 04-04-2012, 02:01 AM   #1
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Base boost questions :-)

O.K, At the risk of sounding stupid and losing the little credibility I had,

What is "base boost"

How do I adjust "base boost"

My understanding is,
If I have a 5lb spring in my wastegate actuator, I'm at 5lb base boost. If I have a 10lb spring, I'm at 10 lb base boost.

Is this right? Do I have any idea what I'm on about?

What is the limit of "base boost" I can run?

Can someone explain to me what's going on, because my head hurts

Cheers
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Old 04-04-2012, 03:29 AM   #2
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You really should know this by now based on all the mods you have. BB is usually set at what your tuner tells you to set it at. On a t5, unplug apc and run car in third or fourth gear and write down how high you BB is. Then you can adjust the wastegate rod by turning it in or out, or use springs. If you have a 10lber then usually this means that bb can not be set lower then 10lbs. So if your car detects knock, etc then the ecu will cut boost to a safe amount, and it you have a 10lber then knock will be cut no lower than 10lbs.
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Old 04-04-2012, 03:57 AM   #3
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Quote:
Originally Posted by lms View Post
You really should know this by now based on all the mods you have. .
Yeah, I know. I'm embarrassed to ask
I've been waiting for someone else to ask this question.

Everybody always talks about it ,but i never grasped the concept.


Sorry, what does apc stand for again


Could you type slowly so I can get it thru my thick head
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Old 04-04-2012, 04:58 AM   #4
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APC/BPC is the boost pressure control valve. If you disconnect this wire and drive, you are running on base boost. You can brake the car and floor it to see the base boost on your boost gauge. You then adjust the rod or use a helper spring to achieve the desired goal. A stock car is around .4 bar base boost. You would want this to be around .6 bar or so depending.

Checking base boost:
http://www.genuinesaab.com/psi/files...ost%20Test.pdf

Adjusting base boost:
http://www.genuinesaab.com/psi/files...20Pressure.pdf
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Old 04-04-2012, 05:03 AM   #5
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Quote:
Originally Posted by bogan View Post
Yeah, I know. I'm embarrassed to ask
I've been waiting for someone else to ask this question.

Everybody always talks about it ,but i never grasped the concept.


Sorry, what does apc stand for again


Could you type slowly so I can get it thru my thick head
Sorry, I'm old school as back in the saab 900 days, I had an 88 spg, the BPC solinoid of today was referred as the apc solinoid of yester-year. Unplug the the bpc, run car hard and the max boost will be your BB which can be adjusted/fine tuned for the mods you have. No two cars are the same, so if your tuner states to set BB at 12psi, this is a starting point. Some say to set BB via the wastegate to stock settings, or if you have a 10lber, adjust to 10, and to not turn it in or out after that. What you use is just springs to adjust BB.
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Old 04-04-2012, 06:10 AM   #6
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Don't turn the waste-gate rod. You'll shorten the throw sufficiently to the point where boost control is difficult and when the ECU needs to dump boost it cannot. Maybe a couple turns is OKAY, but, I'd use a proper spring or a helper spring. Bogan; I'm currently finding what I need in terms of BB for my T28. Seems that the stock WG tension will hold to around 22-25psi.
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Old 04-04-2012, 07:20 AM   #7
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i usually tell people to set base boost at 1/2 of what the WOT pressure should be,, example, if your car is set up to run 16psi, base boost should be 8 psi. base boost is also the safety point for the cars electronics,, if your at WOT the ecu can not control boost below base boost (in t5 cars) so if it picks up a drastic ping, that is the lowest point it can fall back too in hopes of protecting your motor
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Old 04-05-2012, 12:22 AM   #8
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Thanks everybody for excellent answers. I understand what's going on now.
Thumbs up.

I can't wait to fine tune this thing and get it on the rollers
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Last edited by bogan; 04-05-2012 at 12:28 AM.
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