The big problem with many old piston engines is that the octane rating they were designed for is no longer available.
So the engines on historic a/c like the B-29 are now operated on much less than the original horsepower
The Canadian forces operated the piston Argus for many years after turbines had taken over. They had to get a refinery to make up a $pecial batch to keep it flying. The CAF doesn't have that kind of money.