Some good points made in this thread. It's so easy (and quite affordable) these days to hit 400+. With the likes of the TTE hybrids along with the usual 2+ bolt-ons, more and more cars are out there at this state of tune. One side of the argument is that because of sheer numbers there will be more failures to read about than in the days when 400+ was reserved for big money builds with big Garretts. And as Pudding alluded to, these cars weren't all pushing big PSI, high EGTs, and all the other potential issues of using stock exhaust manifolds and hybrid OEM turbos.
That said, I do believe it can be done safely, on a BYD to some extent, but certainly on a CDL. So much of it is down to the mapping. It's not really peak power that's the concern, more the boost/torque delivery. If things are kept sensible at high loads (ie a progressive/flat torque curve rather than letting the boost go through the roof at low-mid revs) it's generally easy and safe to reach pub figures like 400bhp with a hybrid and one of the stronger blocks.
The caveat to all that - in my case at least - is that if and when I go k04 on my baby BWA it'll be done to a very conservative level, with a sensible torque curve, like you guys mention. So 340-350bhp peak power, and peak torque of maybe 360bhp max. A good mapper could quite easily squeeze almost 400lb/ft out of a k04, but on a BWA.... I'd be worried about it all going wrong, however many success stories there were out there!
