Why would (just for example) shortening the prop allow one to raise the
RPM
limit of the engine?

It's bad to allow the prop tip to go supersonic.

Understood.

However, how is it that you can up the RPM limit of a given engine simply
because you want to keep the prop tips subsonic?
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"