True. That's why I assumed the 6.4 used parallel turbos until I saw it.

Yeah, the 6.4 is pretty sweet. At first glance at the motor, it's like where is it behind all that plumbing!?, haha.

I did a bit of looking around and the type of sequential setup the 6.4L has is the kind where one turbo spools and sends the air to another turbo to get multiplied. Apparently it's kind of common on diesels, it allows the engine to operate more smoothly. The first turbo is a small fixed rate turbo and the second is a large variable rate turbo.

I tried to find out if the twinforce stuff is sequential, but everyone is asking the same question. It probably is though since it just makes sense for fuel economy.