If you put houshold air vent louvres in that opening, you will have an excellent low pressure zone. Just a large opening always is uncertain. Sometimes it works, sometimes it won't, depending on very small airflow path fluctuations. With louvres, it will create a low pressure zone for sure, as well as create a larger pressure difference.
More pressure difference is better cooling.
With aircooled gas engines, there is no such thing as too much cooling, because the temperature difference needed for heat transfer must be a lot larger than with liquid cooled engines.
Engines run best with their temperature at about 150F. That is extremely hard to achieve with air cooling in our meagerly finned engines, so we are already happy if temperatures stay below 350F. At that temperature the engine is less happy though, and rewards you with shorter time intervals between overhauls.