Mbc

[tuxx]

Hello,

Been here for a while I have seen a thin red line... MBC's ... In Denmark not many uses MBC's .. "we" let the APC valve do the job.

What's the deal with a MBC? (I know what it is, but what is it that it can do that the APC cannot?)

I have a 9000 2,3CSt... would it benefit of a MBC instead of the APC valve?

Downs and ups?

TIA

[klarking1075]

MBC will not back off the turbo charger in the same way that APC will when things aint going right. This means that you have far more potential for things going really wrong.

However, the plus side is that you are less likely to get the fluctuating boost of a bad BPC. Add to that the boost is easier to increase beyond the normal ECU controlled level.

Kenneth

[tuxx]

Originally Posted by klarking1075

MBC will not back off the turbo charger in the same way that APC will when things aint going right. This means that you have far more potential for things going really wrong.

However, the plus side is that you are less likely to get the fluctuating boost of a bad BPC. Add to that the boost is easier to increase beyond the normal ECU controlled level.

Kenneth

To be a little provocative... you're saying it's something ppl install instead of having a fully functional car? I know I know.. I'm being rough now..

The only upside I can see is increasing boost beyond ECU.. the other issues can be dealt with, with a car that's maintained..

But then again... I haven't had issues yet with my APC system, so maybe it's a pain in the *** when it's not working as should..

What do ppl do then when driving 35degress celcius, octane 95 in the tank and kicking the pedal... With my APC it shuts down the fun due to knocking etc... with a MBC I would have worn my engine excessively...

Is it worth the downs?

[klarking1075]

What I was saying was that you no longer have the safety zone that the APC BPC provides. If things start to go wrong very quickly (ask SaabStudent about this) and you have an MBC fitted, it will quite happily keep full pressure, where the APC system would have reduced pressure to protect the engine.

APC isn't just about increasing boost, it's also a safety item in that it helps to protect the engine from overboost, knock, etc...

In terms of is it worth it, I'd wait for someone else who is not quite so biased in their opinions comes along. Me, I've learned the hard way that safety is paramount (I know, getting conservative in my old age).

Kenneth

[tuxx]

Yes I fully got that, and I'm full aware what the APC does.

And from knowing what the APC does... I don't get why ppl install the MBC ....

So I'm looking for the hard cons that'll get ppl to install something that removes the safetynet below their "linedance"...

[prionailurus]

The best way to use an MBC is to put it inline with the wastegate hose from the APC solenoid, so as to gain a bit in performance, but also retain the safety funcionality aspect of the well designed saab system.

35degC and 95oc fuel, I wouldn't be kicking the pedal, that's asking for detonation. Just plod around sensibly til the weather cools off a bit, and get some higher rated fuel if possible.

[Stefano]

If you have a trionic car, if you use a MBC and you have knock the ECU can still cure it by overfueling and redicing the timing advance. So you still have a little protection agaisnt knock. Older APC cars couldn't do it.

The best way to use an MBC is to put it inline with the wastegate hose from the APC solenoid, so as to gain a bit in performance, but also retain the safety funcionality aspect of the well designed saab system.

Isn't it just the same thing as raising the base boost? I know it's better easier to use an MBC than to adjust the wastegate, but the concept seems the same...

[tuxx]

Okay thanks for your replies.

[prionailurus]

Achtung...possible theoretical nonsense...
putting the mbc in should alter the point at which the wastegate begins to open, which would be at full boost. I'm not sure what exactly an adaptation run does, but my base boost is currently 11psi with the mbc and 6.5 w/o mbc. What I'm thinking is, the adaptation run requires full load thus full boost in a high gear (3rd for my auto) and then depress brake aswell, maybe the system sees the full boost, then sets base boost at half this figure, which would be approximate with the mbc as the max boost isn't stable (mine spools to 20psi quickly then comes back down to 15psi within 2 secs).
a good point stefano, I used to think base boost was purely set by the pre-tension on the actuator rod, but that wouldn't explain the base boost differences between with and w/o mbc.

[Stefano]

Originally Posted by prionailurus

What I'm thinking is, the adaptation run requires full load thus full boost in a high gear (3rd for my auto) and then depress brake aswell, maybe the system sees the full boost, then sets base boost at half this figure, which would be approximate with the mbc as the max boost isn't stable

No if you brake you force the trionic to give you base boost and the adaptation run ends. Base boost is onle machanically set, Trionic don't adjust it. Mechanical interventions on the wastegate actuator, exhaust... stuff like that change it, not the adaptation. Base boost is what you get when the BPC is stuck open, so the Trionic is doing nothing with the boost. Trionic's job is to decide how much boost give you above base boost. Hope this is clear...

a good point stefano, I used to think base boost was purely set by the pre-tension on the actuator rod, but that wouldn't explain the base boost differences between with and w/o mbc.

Because installing and adjustin the MBC is just like changing the base boost (plus other effects at full boost, if you keep the BPC valve, of course), so it's natural to have different base boosts with and without MBC.

[prionailurus]

Achtung...possible theoretical nonsense...

don't say I didn't warn you

Trionic's job is to decide how much boost give you above base boost.

Yip, having thought about it, that sentence just about sums it up, well put.