Thanks for sharing panic - I love the engineering lessons in your posts. Leading to a couple of questions:
(1) Is the resonance frequency and corresponding critical RPM range(s) more important than journal overlap?
I found
your tech paper instructive on this topic. But my memory was leaving me confused by the conclusions drawn about SBC cranks.
I went digging through my library and sure enough in the old Grumpy Jenkins speed manual he discusses at length the retrofitting of the earlier cranks to new blocks:
"In our drag racing engines we use the early smallbearing
327 cranks and a spacer sleeve is required
between the late block bearing saddle and the small
journal bearing. This crank is an especially stiff forging
and the smaller bearing diameter reduces bearing
speed. Adapting this early crank to the late case is
much simpler than it sounds. It is, in fact, extremely
easy. To sleeve down the block we install the late
(large diameter) bearing shells in the saddles and pin
them in place with small roll pins as can be seen in
the photos. These pinned bearings/sleeves are then
align honed to the Chevy recommended saddle diameter
for the early (small diameter) bearings."
(2) If the later cranks with larger journals/overlap are stiffer - was Jenkins trading crank flex for reduced bearing speed?
(3) Was this trade-off specific to his drag application - several seconds at very high RPM?
Curious . . .
