If the Cadillac models with the same engine are running twin turbo intakes and gaining mucho horsepower, how difficult and expensive would it be to get my 2014 Impala ltz up to 400 hp?

 

You would have too buy the parts from GM, Turbos, Hoses, Intake Manifold, Throttle Body, Injectors, Exhaust system is much different, a new PCM or a re-flash of current one if it is compatible, Transmission replacement as the standard 3.6L transmission will not handle the extra Horsepower. All would have to come from a Cadillac XTS as all the other Cadillac variants are designed for rear wheel drive. In a word Very Expensive and Difficult !!!!! And don't expect GM to be of any help if things do not work out properly. It would be easier to just trade the Impala for a Cadillac.