Porsche aero engine
 

Why did the Porsche PFM 3200 engine not catch on?

If you look up what the installation in a Mooney entailed you'll find it blindingly obvious!

Not only what gasax says above but once in it was hideously complicated to work on with complex parts and it was a heavy old lump.
Simplicity won through in the end and Lycoming started producing for them again and then it went to Continental.

From wikipedia I learn that a lot of money was dumped into the project, more than it could ever recover. Perhaps slightly overdone on the "Deutsche Gründlichkeit" bit.

The crank shaft tended to snap, they are very light compared to aero engines and other Auto shafts so that was it's end.