SSD's advice about operating the Gipsy is excellent, and in my opinion spot on for any aircooled aircraft engine. (Though shut down other types with the mixture ICO, but for the same reason as SSD states). I have more experience maintaining Gipsys, than the dozen or so hours I have flying them (Tiger Moth), but I think that you'll find that an abused or failing Lycoming or Continental can be more easily/quickly/economically repaired. Not that any engine should be operated so as to invoke the need for repair, but if the engine has to be run hard, I'd be choosing away from the Gipsy for that flight.