[rrolland]

During my search for a P337, I looked at a couple of conversions. Both were Super Rockets with the IO 520.

What I found is that the useful load was down substantially. On one of them, the useful was 1090lbs. So with full fuel (148 usg), there was not enough payload left for the pilot, unless the pilot was very slim...

My guess is that the weight of the bigger engines plus all the extra equipment such as AC and soundproofing are away at the standard useful load.

These aircraft would do better with a gross weight increase but that brings its own set of issues such as greater wingspan, possible AD inspections not to mention weight and balance management. The max landing weight remains the same.

In the end I found the stock P337 to be a better overall balance of performance and capabilities.