Here's what I found in blown engine number 2....
 

metal shavings the size of a dime. Looks as though someone with a wood plane has been inside the engine?!? This was stuck to the handy magnetic drain plug that I got from LN. Any guesses as to the cause/source of the filings and shavings?

http://i271.photobucket.com/albums/j...a/CIMG0369.jpg

http://i271.photobucket.com/albums/j...a/CIMG0370.jpg

most likely spun rod bearing

It would have to be magnetic - which rules out (most) of the alloy or white metal componants in the engine.....
Conrods, crankshaft, IMS bearing / shaft, timing chains / sprockets, oil pump gears / drives etc, etc.
Looks terminal whatever it is !!

Shredded IMS bearing?

Yep.. Looks like it lost a rod bearing to me, they are steel backed and shed material shaped like this when they fail.

Wow! Any clue how or why that happened?

What track were you at BTW?

My guess would be a rod bearing as well.