700R4s can be built to be as strong as a Turbo 400 and stronger.
Why does the 4L60 and 3L60 (TH350) have the same center support design and low/reverse piston, but the 3L80 (TH400) has the same center support design as a 4L80E? I've built some very badass 700s in my time, some of which regularly see 800HP shooting through them, but I won't guarantee any of them to handle more than 450 HP. All they are is a TH350 with an overdirve unit. However, the TH400 is easily built to withstand 2000 HP on a regular basis. Yeah, I'd have to disagree with the above claim. The class-designation tells all. Would you think a 4L60E is in the same duty class as a 4L80E? That statement is the same as saying a TH350, AKA 3L60, can be built to take as much stress as a 3L80, AKA TH400. I'd stay away from a builder who tells you a 700R4 can handle 1200 HP. Maybe for a little while, but when those things let loose, they can also send shrapnel everywhere. I used to know one of the guys who was on the team who designed the TH350 before he died of cancer. He once told me how during the testing phase, they lost 3 guys when one of those units exploded before they beefed up the floorpan in the test vehicle. Fortunately, I don't think a 6.2 diesel has any chance of breaking a decently built 700, especially if it has the later design of the input shaft (they kept cracking the 27-spline ones when they introduced the 6.2).