Originally Posted by greenplates
Dude just use the search it's soooooooooooo easy to find answers...
since I'm feeling generous
1.) The stock BCS does it's job, but it gets tired and full of crud. Thus, stops doing it's job as well. This may lead to fluctuating boost.
You can remove the stock BCS and clean the ports. By attaching a battery to the positive/negative terminals on the BCS, you will physically open the solenoid and be able to clean the entire port.
2.) The wastegate DOES do it's own job. But mechanical boost is only controlled up to 7psi. After that, the BCS dials the boost according to air/fuel/etc.
3.) MBC are cool on honda's, not on a Subaru
Just sounds like some german engineering to me, a little overcomplicated for such a simple system.