I'd run it without the Dawes if I were you, you really shouldn't need the Dawes. Remember that the Dawes disables the Trionic's boost control operation and since the Stage 3 upgrade in altering that part of the software setup it's best to run with a standard solenoid imho.
Alan B was running a Stage 3 and Dawes device on his Aero and it ended up dangerously lean. Best to play it safe and not have to be sorry.
Perhaps add a Dawes later on, if you really really need more boost. Save up for a big turbo and do things properly.
MBCs are really a slightly risky thing to use (Dawes particularly if set too high)- the reason Saab turbos are so reliable is that they use APC and back things off when necessary.
Using an MBC for lowish boost value is OK, but using one in search of higher performance is fraught with risk- unless you're taking other measures. When I used one for fairly high boost (up to 1.5 bar) I compensated for that by fitting water injection, which has two important benefits- controlling unwanted detonation and lowering EGTs. Even that was slightly risky, as that boost level is likely to have been outside the mapped range of the ECU software.
Speedparts and Maptun higher level upgrades use base boost pressures little above stock spec in order to ensure that they can retain adequate APC. Raise the base boost too high and the APC may not be able to reduce the boost sufficiently under problematic conditions.
After trying many variations and ending up with a Maptun Stage 5, I am convinced that the way to safely and reliably get more performance out of a turbo Saab is under software, not hardware control- and I reckon that Trionic is quite simply the best system to do that.
I use the dawes in low boost mode where it gives really good grunt at the low to mid rev levels
however I have backed the max boost to 1.2 bar and
the way I have it configured the apc still gives protection...(this is with the abbott ecu)
the dawes is put into the line from the solonoid to the wastegate..
it works for me
I will be taking it out when I do my maptun ecu as the programm will give you full protection..
I agree with Mark E. The ecu needs to be able to control the boost and dial it back whem pre-detonation is sensed. Also, from experience, adding the mbc will greatly enhance low rpm torque, however, as egt and intake temps rise and perhaps pre-detonation is detected, the ecu severely retards timing and upper rpm performance becomes much weaker. So my opinion is to stick with ecu control.
I basically agree with Mark and would say, if you can afford it, software wins over a (crude) hardware soution.
Having said this, I do run an MBC with the Speedparts stage 3 and have done so for the last 6-7k with no problems. Max boost has been set at 21psi - which is a shade higher than Speedparts stage 3 max boost. As Mark E says, you are taking a risk doing this sort of thing since, with this set up, the only way that the trionic system can deal with detonation is by retarding the timing. A water injection system is an absolute 'must' with such a set up. I am building my one right at the moment.