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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 09-29-2009, 03:13 PM   #1
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MBC on t7 ?'s

I was always under the impression that t7 wouldn't get any benefit from an MBC? But my dad mocked up a DIY mbc, and I hooked it up and it DEFIANTLY makes a difference, as in 10 psi difference. Without the MBC my boost gauge said that I was boosting 5 psi, now it holds a pretty good 15 psi in all gears. I thought it was a fluke but it's been staying like this for over 2 weeks now. I'm not arguing with obvious results i'm just looking for some imput.
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Old 09-29-2009, 03:31 PM   #2
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Old 09-29-2009, 03:59 PM   #3
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What I think to be bone stock 2000 9-3 Base.
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Old 09-29-2009, 04:26 PM   #4
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Ehhh scary to me... T7 with MBC pushing 15psi without the added fuel on lightweight pistons. Yikes.
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Old 09-29-2009, 05:08 PM   #5
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I thought T7 would safely boost over 15psi. if the conditions were ideal. Cheap/safe tunes will run you $300 and thats less than a set of pistons.
my .02.
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Old 09-29-2009, 05:10 PM   #6
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I thought T7 would safely boost over 15psi. if the conditions were ideal. Cheap/safe tunes will run you $300 and thats less than a set of pistons.
my .02.
Yeah, they will... but something about using an MBC scares me as the car isn't getting the amount fuel it needs and when it needs it.
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Old 09-29-2009, 05:15 PM   #7
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Oh I understand that. I believe the MAF (if its in 100% new cond.) will see the added demand in airmass and try to give it fuel. A new 3.5 bar reg. might buy some time.
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Old 09-29-2009, 07:51 PM   #8
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You should have the CEL code for a malfunctioning boost solenoid control valve.

It's 100x safer to pony up for a tune or at least some time with T7suite and to keep the BPC in there so that boost, fuel, and timing can all be controlled properly by T7 to maximize the power that can be put down with the minimal amount of knock.

With T5 it was "safer" to run a MBC as it wasn't as picky since you didn't have a MAF to meter air entering the system. With T7 it's a case of playing with a fire the size of a California forest fire because the instant that MAF starts going out of spec then your screwed as any adjustment for fuel and timing won't be right and you'll be pinging away at 15 psi till it either bends a rod, cracks a piston, etc.



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Old 09-29-2009, 07:59 PM   #9
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whats scary to me is that its "bone stock" with no exhaust upgrades and he is trying to push the boost up to 15psi. EGTs anyone?
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Old 09-29-2009, 09:13 PM   #10
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Your car was probably boosting 5psi for a reason. Bad fuel, hot day, high egts, something!

I saw a T7 the other day with a severely cracked piston-the pieces ended up getting chewed up by the turbo, wonder what happened to the turbine? his piston pieces were melted into the turbine housing. Not to mention what happened to the rest of the motor. This is too common on T7 cars. Good luck.

Try to figure out why you were only boosting to 5 psi and fix that problem before "correcting" it with an mbc. just my .02...

EDIT: My 2000 9-3SE would boost to 20psi up at elevation (11,000 feet), and up to 15psi at sea level with only gs's 3"downpipe. 15 is okay for stock T7, but if your car wants to boost to only 5psi, there is a reason for that.
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Last edited by J93O; 09-29-2009 at 09:18 PM. Reason: forgot to mention
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Old 09-30-2009, 02:58 AM   #11
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I don't know.. It's always boosted 5 psi, I'm not correcting anything. It was like 45 degree out yesterday also.
There's no new knocking, cel's or anything. hmm, and the 15 psi is too fun to let go of with no bad symptoms yet.
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Old 09-30-2009, 04:10 AM   #12
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I don't know.. It's always boosted 5 psi, I'm not correcting anything. It was like 45 degree out yesterday also.
There's no new knocking, cel's or anything. hmm, and the 15 psi is too fun to let go of with no bad symptoms yet.
Well, the least we can do is tell you about the effects of doing that on your car. It is very risky that setup, but if you think it works then I hope we don't see a melted pistons thread.
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Old 09-30-2009, 06:30 AM   #13
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Your car was probably boosting 5psi for a reason. Bad fuel, hot day, high egts, something!

I saw a T7 the other day with a severely cracked piston-the pieces ended up getting chewed up by the turbo, wonder what happened to the turbine? his piston pieces were melted into the turbine housing. Not to mention what happened to the rest of the motor. This is too common on T7 cars. Good luck.

Try to figure out why you were only boosting to 5 psi and fix that problem before "correcting" it with an mbc. just my .02...

EDIT: My 2000 9-3SE would boost to 20psi up at elevation (11,000 feet), and up to 15psi at sea level with only gs's 3"downpipe. 15 is okay for stock T7, but if your car wants to boost to only 5psi, there is a reason for that.
It is kind of interesting to watch the airmass vs boost on hot and cold days or at lower and higher elevation, you will find, or at least I did, you can make the same say stg 3 airmass of 1280 with 15psi and then you can make it with 20psi on a hotter day or higher elevation, same thing, density altitude. As you climb, its just like having higher temp air.

I always tell people to watch airmass and not boost because you can on some occasions, really cold morning with thick gooey air, make the requested airmass with much less boost.

John
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Old 09-30-2009, 08:22 PM   #14
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That's very true John, and you know way more about this than I do, but I never saw less than 11psi on my 9-3 even on 90 degree days. Doesn't 5 sound low? I don't think his issue is that he was getting super cool air all the time and only boosting 5psi but making the same airmass, but that some other issue was causing him to boost less and making less airmass and getting worse performance, which is why he was unhappy.
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Old 10-01-2009, 12:04 PM   #15
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Best of luck. My guess is something was wrong like the BPC. But T7's are ellusive to me.
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Old 10-01-2009, 05:11 PM   #16
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My guess is the BPC valve was bad causing only 5psi. If you stick a bolt in the top hose, and it runs better, then you know it was bad.

From what i know, if there is any problems with a MBC your car will go into limp home mode. Then you back off the MBC.

Check out smart performance to get the details, but they say that a MBC never blew up an engine if set up right. Now if it's not set up right, anything can lead to problems.

The tune is a better choice, but cost more.
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