Porsche went to twin turbos, well because they can. I wish I was smarter than the Porsche engineers but that just isn't the case, not by a long shot.
They have the R&D to design the system so that it works. But.... I stand by what I said, they are not getting more power out of twin turbos than they could get out of a single turbo. What they are getting is a system that has less lag and a lower threshold limit. As I said that is the advantage and it takes serious engineering to pull it off correctly. Just grabbing a couple of turbos that look right and bolting them on will probably not get the desired result when it comes to threshold and lag.
Porsche also went twin turbos on their six cylinder engine, not a 4.
In order to run a twin turbo setup on a type 4 you would have to run cylinders #1 and 3 to one turbo and cyls #2 and 4 to the other due to firing order, not an easy thing to do. Someone please correct me if i have those numbers wrong, it might be 1&4 and 2&3 but that doesn't sound right.
The big monster turbo, the 935 used a giant single turbo and made huge power. It also shot really neat flames