[urq] turbo question

[urq]

... I'm by no means an expert on what makes turbos go boom, but for the sort
of immediate failure you are reporting I can't imagine there's any sort of
build up of anything ... the first thing I'd suspect is that the turbo is
overrevving.  Are you sure that the wastegate is operating?

Steve B
San José, CA (USA)

-----Original Message-----

A friend of mine who has no access to internet has asked me for help. He has
a sport quattro replica (lucky chap) but has recently suffered a series of
kkk turbo failures (not so lucky). In all instances all damage has been down
stream of the engine i.e. no damage to the engine. What happens is the
exhaust side explodes (literally) throwing bits of metal everywhere. 
The engine is a finely tuned 20v, running modest boost but dyno'd at about
500bhp - prior to all this. The failures have come after virtually no miles.
In one case, about 20 yards off the start line after last rebuild.
The oil supply to the turbo has been checked and given the all clear. No
bits in the oil. Datalogging shows no curious changes in mixture (leanness).
The things just explode. All bits go down stream. Engine strips revealed no
damage - I think I said that already.
To me it seems like exhaust isn't flowing enough when at WOT causing
pressure build up, heat build up and bang. Doesn't seem possible though.
Prior to each failure, it runs smooth, no smoke, no noises, no water temp or
oil temp rises. Weird.
Any ideas what could be causing this? His bank manager is starting to ask
questions....