You mentioned never hearing of an aircraft engine producing one horsepower per cubic inch (Can you have more power and reliability? Jan. 28 issue).
How about those Wright compound R-3350s of 3700 hp? These great engines powered Douglas DC-7s, Fairchild C-119s, Lockheed Super Connies and P2V Neptunes, etc.
I flew PV2-Vs with these and we often got 2,200 hours between overhauls. Yes, they were temperamental, 145-octane fuel and “water injection” above 3,400 hp. I have shut down and feathered my share of these for prop and accessories problems, but never for a “core engine” problem. And, they had a “specific fuel consumption” of 0.37 lb/hr/hp! Compare that with modern engines, even diesel!