Radiator/cowling flaps

[horseback]

I believe that in most cases, the main limiting factor for water injection for the R-2800 was the water available in the water tank. Whether the tank's volume was determined by space or the amount of abuse the engine could safely take in a single flight, I cannot say, but I do know that if you went to water injection/War Emergency Power, you were supposed to inform the aircraft's crew chief, who had to make several checks and tests before clearing the aircraft for its next flight (and often would say unflattering things about you if your reasons for the extra work seemed insufficient).

cheers

horseback