The 8cm housing is more suited to a 2.5 , it will be laggy on a 2 litre you need a 7cm to keep the lag to a minimum.
Don?t get hung up on numbers , as mentioned before your car could make 300 on one dyno and 350 on another.
400hp is a tough one to achieve from my experience.
Forging the engine alone won?t give you any more power just reliability at the extra power .