400 is just a number. Almost any motor can make this number with the right parts. Some take more factory parts to be changed to get there though. Stock turbos may be a tad challenging to get to 4oohp but its not too far fetched to make it happen with more time in development but you will be running these turbos at maximum efficiency most likely which will degrade their life expectancy. 400hp would be easy with different turbos and the right tuner (easy is not meant to be interchangeable with "cheap").
2008 BMW 535XI WAGON
Sapphire Schwarz on Schwarz