<<re:.....I find the smoothest operation above 2600 rpm, acceptable in the
2300-2550 rpm, and ugly in the below 2200 rpm range...
I rest my case!.
Jack Kane>>

I don't know if Jack would agree, but I think that torsional vibration is
just like a bullet - you don't feel the one that gets you.  A torsional
vibration is just that - twisting of the crank and it doesn't make itself
felt in the airframe.  But how do you do a "vibration survey?"  At the front
it is easy because of the starter ring gear, but don't you also need to put
a mag pickup at the rear?  On a Lycoming engine there is no access.  How do
they do it?

Gary Casey