Posted for "Jim Nordin" <panelmaker@earthlink.net>:

 
 You know Lorn, sorry I don't know the answers to your questions. And the
 comment by the 421 vendor is interesting too ... but I suspect they had no
 more empirical data than anyone else since it hadn't been done but were
 trying to impart "practical ideas" on how to preserve your machinery. Where
 the 20-50 hour numbers of engine life came from is anybody's guess. Did
 anybody ask for the data that supported that claim? I doubt it .. but rather
 buyers took it from the vendor as friendly advice that likely couldn't hurt.
 Airplane sellers after all want to impart some semblance of knowledge and a
 friendly bit of advice would hopefully bring trust and allegiance from the
 customer.
 
 Prop driving engine. I have no idea. But in the early life of the engine
 when breaking the cylinder walls in, I'm almost certain the correct method
 is to "seat" the rings with power applied. After "seating" is established, I
 wonder if there is any harm can come from the prop driving the engine short
 term, as in letdown or on final. I guess Lyc and Cont must have performed
 those tests to TBO and found that to be true. I'm impressed they would do
 that.
 
 Backfiring? I think that's not abnormal for some engine types. I know Lon
 Kelley's L-ES and many similarly powered Bonanzas make a lot of noise on
 final.
 
 
 Jim