Posted for "George Braly" <gwbraly@gami.com>:

 That is NOT detonation.
 
 It is something else.   Probably a cylinder momentarily quit firing and a
bunch of fuel ended up in the exhaust system.  BANG.
 
 Maybe.
 
 You should carefully check the turbine blades for damage.
 
 Consider overhauling your magnetos.
 
 You are not the first person to report this in IV-P's.
 
 Regards,  George
 
 

"""
 a question to those savy in engine matters: this am
 while flying at FL210 in the clear OT  -10 engine
 leaned to 16 GPH all parameters normal CHTs 330 more
 or less TIT 1640 270 kts going east suddenly the
 engine detonated, one loud bang lasting 1 second, no
 change afterward with all numbers again unchanged.
 landed home HQZ and inspection revealed nothing.
 drained fuel myself no water, oil level ok, engine
 performance did not change after detonatiion. TT 260
 HRS. any ideas?
 andres regards
"""