Variable vane turbos will provide boost without excessibe heat over a much wider range than normal turbos. In other words if you have a turbo vehicle that doesn't "get up and go" until 2500rpm the same size variable turbo will "get up and go" at 1500rpm while still giving the same boost and no more heat at 3500rpm.

Porsche, Mercedes, Volvo, several semi companies and most foreign makers(all those diesel models europe gets that we don't) seem to have no trouble with them. I suspect it's another Ford problem, not Garrett.

Personally I believe the new 6.4 engine is for more power to combat the new pollution crap and also due to lost faith in the 6.0 by many formerly loyal Ford owners.

Sequential turbos require very complicated plumbing, quite a bit of space, and enough valves that computer control is almost mandatory. My vehicle is not computerized. I'd like to keep it that way. Not to mention I don't have a lot of spare space under the hood.

__________________
I suggest we solve high gas prices with environmentalists... unfortunately they don't burn well.
1982 300CD, 220K miles: This vacuum system will be the death of me yet! (OBK #26)
1977 F150 400 C6 2wd, 10.2 sec 1/8 mile with 2.75 gears.
1965 Mustang. Mostly stock... LOL!
2001 Ram 2500, cummins, 5spd, 202k miles.(girlfriends)