It has nothing to do with Rich or Lean. It has everything to do with operating temperature. The running fits of ABC engines are designed to be correct at operating temperature, not when the engine is cool.

The engine can be run as rich as one likes provided it is bought up to operating temperature and rpm. I break in my racing engines rich but at 24,000 rpm. That rpm is the end use rpm and it will come up to temperature. I use a break in prop that has been cut down to give me the rpm and temperature at a rich setting.

Anybody who claims this is all "Hogwash" has obviously never operated high performance engines. As has been said the average ABC/AAC sport engine does not have the tighter fit of all out racing engines and will be a bit more forgiving during the early runs. However if the same principles of care and attention to detail that are applied to high performance engines are applied to sport engines it will not be detrimental to the engine or "Hogwash".

Ed S