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

 Rob,
 
 Our research at GAMI is largely the source of the data which Walter has seen
and to which he is referring.
 
 As part of this research,  about six years ago,  I ordered up a complete
 SDR, Accident report, NTSB report history on every “detonation” or
“pre-ignition” related accident or incident in the data base since about 1970.
 This was/is a stack of printed paper a couple of feet high.
 
 I then went through and analyzed all of those,  trying to identify and
understand the issues.
 
 I did this in light of direct evidence we have from operating engines well
into medium to heavy detonation for significant periods of time - - without
injury to the engine… upon later tear down inspection.
 
 The more recent advent of recording downloadable  engine monitors has
provided a whole series of data files in which there is clearly established
 pre-ignition - - that resulted in damage to the cylinder that most closely
coincides with the description of the damage to the cylinders from almost all
of the old accident reports that assert that “detonation” was the cause of the
damage to the engine.
 
 As it turns out,  EI,  Insight, & JPI all have erroneous descriptions in
their pilot manuals as to what the pilot should see in the event of
“detonation”.    They even contradict each other and, still, none of them get
it right.
 
 The fact is  - - - pre-ignition is characterized by  significantly falling
EGT and rapidly rising CHT on a cylinder ( one degree per second or one degree
per two seconds).   Period.  Parade rest.
 
 Detonation,  mild to moderate detonation - -  deliberately induced on the
test stand - - results in  zero to minimal  declines in EGT and a rather
gradual increase in CHT (compared to pre-ignition).
 
 Spark plugs appear to be a major culprit in pre-ignition.   If you drop one -
- replace it.    If you do have detonation,  replace the plugs,  as they can
be damaged by the detonation… when everything in the cylinder appears to be
normal.
 
 Regards,  George