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Old 05-28-2009, 06:06 PM   #1
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MBC Question

I have a cheap Ebay MBC sitting around I want to try out (for a bit!) on the SPG. Thing is, i've heard conflicting reports on where to install it. It seems the most sensical place would be inline between the APC solenoid and wastegate actuator, but I'm not sure. Any advice on this?
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Old 05-29-2009, 03:08 AM   #2
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between the line coming out of the turbo compressor and the line going to the wastegate. also make sure you install it the right direction. i dont what style you have but make sure the boost pressure pushes against the ball in side
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Old 05-29-2009, 06:50 AM   #3
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i'm not sure I understand what you mean by being between two different lines...
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Old 05-29-2009, 07:12 AM   #4
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You've already got a smart electronic boost controller in the car stock.

Why not just tweak the pots on that a bit or even do the 900aero mod?
You are losing all the benefits of the APC system by installing a MBC.

Also, make sure to get a calibrated boost gauge installed before messing with any of that.
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Old 05-29-2009, 10:00 AM   #5
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i have a calibrated boost gauge already

i've tried APC mods and for the time being they haven't done anything - replaced the R40 with a wire and did a 1kOhm F-pot, no extra boost. I think i need new plugs/wires. I just wanted to try the MBC out to see how it works.
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Old 05-29-2009, 10:15 AM   #6
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hmm, what boost are you getting right now? (with apc hooked up)

If you aren't getting the pressure you think you should with the stock/tweaked setup, then you probably have other issues that you should address before tweaking the boost anymore.
just my humble opinion

You were the one that was posting about the noisy solenoid right?
Find out why that thing is working overtime before messing with a MBC.
It could be saving youre ass from a grenade
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Old 05-30-2009, 09:16 AM   #7
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Quote:
Originally Posted by deltronSPG[ATL] View Post
hmm, what boost are you getting right now? (with apc hooked up)

If you aren't getting the pressure you think you should with the stock/tweaked setup, then you probably have other issues that you should address before tweaking the boost anymore.
just my humble opinion

You were the one that was posting about the noisy solenoid right?
Find out why that thing is working overtime before messing with a MBC.
It could be saving youre ass from a grenade

you have a point. I'll post my progress on that issue in the other thread.
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Old 12-20-2011, 09:15 AM   #8
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Just reopening an old thread . I dont have an apc solenoid so till I find one I was thinking of going with a mbc . Car runs at a good steady 6 pounds and has a large intercooler and I have a calibrated boost gauge .Previous owner must have had something going on .I thought just a couple of pounds extra would be safe and install a knock led to keep an eye on things .
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Old 12-20-2011, 10:29 AM   #9
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I ran MBC's in two c900s, both were very modified with wideband o2 gauges.
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Old 12-21-2011, 06:01 AM   #10
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ive run mbc's before, i really see no issue on a c900, because the stock apc setup is so poopy.

although these days ive had better luck just using a monster helper spring on the wastegate, and runnig the C-line directly to the wastegate, 14psi of wastegate presure FTW it never surges, overboost, or any of the traits MBCs are known to have,

the biggest issue with an mbc, or mechanical boost control setup, is the owners desire to crank the pressure up, way beyond what the car can handle, if you stay within reasonable limits than youll be just fine
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Old 12-21-2011, 11:45 AM   #11
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Quote:
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the biggest issue with an mbc, or mechanical boost control setup, is the owners desire to crank the pressure up, way beyond what the car can handle, if you stay within reasonable limits than youll be just fine
this
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Old 12-23-2011, 05:22 AM   #12
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Okay will tread carefully how does an extra 4-5 pounds sound , okay with stock fpr and injectors and larger sidemount IC? . Is that within reasonable limits or is that asking for trouble ?

Last edited by gustav; 12-23-2011 at 05:31 AM.
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Old 12-29-2011, 08:59 PM   #13
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although these days ive had better luck just using a monster helper spring on the wastegate, and runnig the C-line directly to the wastegate, 14psi of wastegate presure FTW it never surges, overboost, or any of the traits MBCs are known to have


So you're saying you can run the line from the compressor housing to the wastegate and it provides 14psi steady? I was thinking of bypassing the APC but also running a knock light just to simplify this car for the meantime while I sort other stuff out. This sounds like an easy solution. Care to elaborate?
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Old 12-30-2011, 11:11 AM   #14
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Just unhook the vacuum line from the APC solenoid to the wastegate.* Instant boost!

I actually did this to diagnose a problem in my old SPG, and left it that way for a while. Just be smart with your lead-foot, and you won't blow anything up.
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Old 12-30-2011, 04:01 PM   #15
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Ahaa I don't trust my lead foot! I did unhook the control valve and plugged that when I was doing some troubleshooting on my APC but was afraid to push it too much into the red. What is a safe place for the needle to go? I have a boost gauge in the mail and I know the stock gauge isn't that accurate but is 1/2 into the red generally a safe spot on high octane fuel (the only type I use)? I do have larger red top injectors as well, but no fuel chip to run them.
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Old 12-31-2011, 06:06 AM   #16
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im surprised the reds idle with no fuel chip, usally the car shits a brick with them in..

yes, you can run the compressor line directly to the wastegate,, It will run whatever your base boost presure is,

increasing the boost is simply turning up the base boost at that point in time, Which can be done by putting a helper spring on the wastegate,, You do not want to crank the wastegate in to much, because it will loose its ability to travel, however a spring just inreases tension, and DOES NOT restrict the wastegates range of movement.

Volvos, many diesels, older audis, and pre APC saabs all had boost controll setup with just the wastegate... no electronic regulation valve
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Old 12-31-2011, 12:30 PM   #17
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Hey thanks for the insight Mike D. I should have been more clear on the injectors...I don't have them installed right now but they are on the shelf for future plans. Everything is stock except for I just noticed the PO must have added a 3bar fpr, which is nice.

I think I will go that route then and slowly increase the wastegate pressure to where I have no knock and call it good. So the spring just helps the diaphram out then? It keeps the flapper shut a little more reliably? Thanks guys!
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Old 01-01-2012, 07:00 PM   #18
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Saab designed a good boost control built right into your car and you are going to bypass it...?
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Old 01-01-2012, 07:51 PM   #19
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Yea the APC system is great when it works as it should. I will get it going eventually (tests show that my pressure transducer is kaput), but for now I'm just playin around.
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