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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 05-06-2004, 09:23 AM   #1
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Raising the boost!!

Ok, I have got a few questions about ECU's and boost control. I was wondering how safe adding a manual boost controller really is? I know this is going to start a heated discussion, but i have to get some opinions. I know a lot of you guys have MBC's, but the thought of raising boost pressure in my Saab to 20PSI kind of scares me. I really would prefer not to blow the head gasket or head. What are the actual specs that a saab 2.0L motor can handle for boost pressure? My question about ECU's is this, say you have stage 3 mods done to your like a 3" downpipe and filter ect., would you request a stage 3 ECU? Are there actually different ECU's setup for different modifications? Your reply's and answers to these questions (that have been driving me crazy)are greatly appreciated!
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Old 05-06-2004, 10:28 AM   #2
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I personaly had a nicely modified NG900 with an Abbott ECU that was adjustable through the Abbott 12 psi wastegate. With this ECU the original owner had his 900 bosting 28 PSI without any problems. I had it closer to 24 PSI. As for the MBC if I understand correctly it does not increase boost, it just liberates the boost you have. You are still limited to 15 psi with tthe factory ECU and an MBC. The MBC is just there to allow you to use the full 15 psi in first and second gear. If you adjusted the MBC incorrectly and you overshoot the 15 psi limit then your car will simply go into limp mode and you will have no boost until you turn the car off.

As for purchasing an ECU, the best way to do it is to talk to the person modifying the ECU and tell him exactly what upgrades you have and what you hope to achieve with the ECU and they should be able to tailer the ECU to your specifications.

I hope this helps you a bit,
Matthew
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'00 9-5 Aero
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Old 05-06-2004, 10:49 AM   #3
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Quote:
Originally Posted by MatthewB
As for the MBC if I understand correctly it does not increase boost, it just liberates the boost you have. You are still limited to 15 psi with tthe factory ECU and an MBC. The MBC is just there to allow you to use the full 15 psi in first and second gear. If you adjusted the MBC incorrectly and you overshoot the 15 psi limit then your car will simply go into limp mode and you will have no boost until you turn the car off.
That is correct to an extent for T7 cars. The T7 ECU can control "boost" by limiting flow through the throttle body, since the throttle is electronic. Thus, even if you remove the ECU from direct control over boost (by replacing it's solenoid boost control valve with a manual boost controller) it still has a way to limit boost to the factory max setting, meaning that there's virtually no way to raise the max boost over the stock setting by only installing an MBC.

For T5 cars, the throttle is manual - i.e. a physical cable that the computer cannot control. So, if you take the ECU out of the boost control loop (by installing an MBC) you leave it with no way to control boost at all, except for cutting the fuel with an overboost cut point. I'm not sure what that cut point is on T5 cars, but it's pretty high.
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Old 05-06-2004, 11:04 AM   #4
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My understanding with the T5 is that it is still limited to 15psi with the factory ECU. At least that was the information I had found when I originaly purchased the MBC for my '96 NG900 SET.

It is quite possible that my information is incorrect. Anyone know for sure?
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Old 05-06-2004, 11:27 AM   #5
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Yea NG900 T5 has a fuel cutoff at 15.5 psi. So if your using a MBC, don't set it past 15.
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Old 05-06-2004, 11:51 AM   #6
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Yea NG900 T5 has a fuel cutoff at 15.5 psi. So if your using a MBC, don't set it past 15.
Ah. I didn't realise it was that low. That kinda sucks!
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Old 05-06-2004, 03:00 PM   #7
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Thanks for the help guys! I was wondering what the ups and downs are to setting the boost to 15 PSI in first and second gear. Obviously better response but I'm more interested in any downs if there are any. Also does anybody have any idea how much boost pressure a Saab motor can handle? Not that I am trying to push my car to the boosting limits but i would just like to know. Thanks
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Old 05-06-2004, 06:10 PM   #8
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I haven't had any problems. I run 15psi, and aside from dangers from misshifting, I don't run rich or lean, and engine sounds quiet as a mouse.

The engine can definately handle over 15. With a mapped ECU, some cars run as high as 28 psi.
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Old 05-06-2004, 07:15 PM   #9
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Well you guys have convinced me. Once my car is running decent (the car needs a new O2 sensor causing it to run lean) I will invest in an MBC. One other thing I was wondering was if anybody on this forum uses one of those apex-i boost controllers?
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Old 05-07-2004, 03:46 AM   #10
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To answer the question about how much boost the stock engine can take. As I mention in my first response I have heard of people boosting at approx. 28 psi and I was boosting somewhere around 22-24 psi. This was done with stock internals but my intake, intercooler, and exhaust had been modified/upgraded. Granted I was only set-up like this for about 6 months before I got T-boned on a highway (stupid Suzuki driver!!!) so I can not comment on how long the engine would last with this level of boost.
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Old 05-07-2004, 04:28 AM   #11
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One other thing I was wondering was if anybody on this forum uses one of those apex-i boost controllers?
If you're talking about the AVC-R, don't waste your money. An MBC will get you 85% of the functionality for 15% of the cost. If you've got that kind of money to spend, go check out the SQR/Maptun group buy!
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Old 05-07-2004, 06:28 AM   #12
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That thing seems pretty serious though. Those Japanese know their turbos.
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Old 05-07-2004, 06:38 AM   #13
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All it does is control the soleniod on the line going to the wastegate.

If you want to be able to dial in precise settings for what the wastegate sees under a wide variety of conditions; and do it all through a pretty, bright blue LCD display interface, then go ahead and pop $500-$600 down for one of those.

If you want to turn a knob on a valve under the hood to a certain position and have that set your boost, then spend $50 on a MBC. You might have to deal with a bit of fluctuation and the remote possibility of boost spikes (depending on other mods) but the Apexi unit isn't going to somehow magically massage tons of extra performance out of your engine, and if you're smart about picking and tuning the MBC, it's not going to do a worse job under the majority of conditions.
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Old 05-07-2004, 06:49 AM   #14
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You can defeat the overboost protection of the stock system if you want too.
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Old 05-07-2004, 07:33 AM   #15
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Quote:
Originally Posted by Brad
You can defeat the overboost protection of the stock system if you want too.
How is this accomplished, and will the ECU still allow for adequate fueling past 15.5?
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Old 05-07-2004, 08:08 AM   #16
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Well I am going to purchase an MBC, I was just wondering if anyone was using the apex-i one.
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Old 05-09-2004, 06:34 PM   #17
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Quote:
Originally Posted by Blaque_Out
Quote:
Originally Posted by Brad
You can defeat the overboost protection of the stock system if you want too.
How is this accomplished, and will the ECU still allow for adequate fueling past 15.5?
It is accomplished by using a voltage clamp on the output signal if the map sensor. The fuel system will not deliver more fuel. I am using a voltage clamp on a 1995 tubo with a manual boost controller. It has seen as much as 1.8bar.
Fuel is supported with two addtional injectors drive by a programable injection driver.
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