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Discussion Starter #1
Ok, my boost guage never gets further than 2/3 of the way up the orange section, so I've taken the plunge and ordered a Forge MBC. From what I've read so far, the 'safe' option is to fit it in-line between the APC valve and the wastegate to delay wastegate opening. Correct?

If that's the case, what do I do with the third connector? Does it need to be blanked off, or is it a vent?

Also, I'm looking for a conservative all-year-round setting on this, can anyone give me a ball-park number of turns to set it to to get me started, or do I really need to get an accurate boost guage? I think I know the answer, but I'll ask anyway...

MTIA,
Alan
 

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i did have an MBC,but removed it for another way of encreasing boost without loosing the APC protection.i left all the vac lines to the solenoid on the rad conected,but cut the hose that goes to the wastegate.i then cut a two inch piece of copper pipe thats a tight fit into the hose.i drilled a small hole in the pipe and pushed say 3/4 of it into each end.this left the hole exposed to the atmosphere.this leaks a little pressure that would normally go to the wastgate to open it,thus encreasing boost(works a treat).the bigger the hole encreases the boost so start small!!!
simon
 

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You're both describing the same thing- ish.

Fitting it as you suggest Alan will enable you to vary the amount of bleed you introduce- but using the screw rather than a drill, whic his clearly a one way process. The bottom port of the "T" does not need to be connected anywhere.
 

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If the boost isn't getting where you expect it to be, it may be because of detonation. In which case forcing it to go higher could be detrimental to your engine!

I'm not trying to scare anyone, but do be careful. Any time you tamper with boost you had best know exactly what you're doing and be quite careful to listen for knock.

Another method for raising boost with your APC is to do some minor electronic mods to the insides of that APC box. But that requires a bit of skill with soldering etc, and is likely best left to professionals. Still, it does offer more protection than the standard MBC does. Worth noting at any rate.

Dubbya~ (Soon to possibly acquire a 1989 900T with 109K miles, for $900
)
 

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i know not where to find info on DIY APC mods, but i do know that saabperformanceparts.com does offer an APC upgrade... i have one on my car but alas, i cannot yet give any feedback about the
increase as i am awaiting a new fuel pump to arrive in the mail before i get the car back on the road.

yes, i am still dealing with the 'no start condition' i posted in the '900' section, just a lack of monies and an excess of work has left me no time to work on the car
 

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I got my info from www.900aero.com ... they have a section on DIY APC mods. For the moment my computer won't open the site, but I think that's an issue on my end.

The APC mod could be a little tricky, and you're taking your engine's life into your very hands, but it does allow for simple tuning. To be honest it looks like fun, but you can get a modded APC for not too much dosh from a reputable tuning company as well.

Not sure how safe it will be. Like I said, if the APC is backing off the boost, there is likely a reason. The reason should be addressed before trying to up the boost.

In other words make sure everything is in proper running order, and your fuel is of sufficient octane before attempting to change how the car runs. I know it's been said before, and may as well be common sense, but it's worth saying again.

Dubbya~
 

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Discussion Starter #8
Thanks for the feedback guys. Simon, I love the copper pipe idea - genius
Although the MBC is already ordered, and I would only have drilled too big a hole anyway.

Should I expect much improvement in spool-up using the MBC this way? Is the MBC an on/off device, or does it gradually open up? Does that make sense?

I take the point about the APC backing off the boost for a reason. I'm currently working on the assumption that I'm only getting base boost due to a fault somewhere in the APC system, but I might revisit this and do some more investigation before finally installing the MBC.
 
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