You will need to have the standard ECU remapped because they wont make 400bhp on standard parts, probably uprated injectors and turbo to make 400bhp, and no its not worth running it with out it being mapped, wont do the car (or engine) any good

though on a plus point, its not exactly expensive to have either the GEMS remapped or the standard ECU remapped (about 600 quid for an ecutek remap).
Tony