350 - 400 will be pushing past the TMIC capabilities - so you will be looking at FMIC bigger injectors an uprated fuel pump... I rescued this from an old thread that we may have lost in the recent hiccups so unfortunately I cannot credit the member who originally posted it...
Just a bit of weee advice if your planning on running big power and im not trying to put you off its just ive looked into it , STI internals and closed block are good for over 450bhp if it has Forged internals, standard cooler is good for 300 maybe more, STI intercooler is good for over 350 but by this stage most start to Run front mount intercoolers but beware of the lag.
Turbo again is down to preference but steer well away from the over priced billet turbos from Scooby clinic ( which arnt even made by them they are imported and have there names added) id be looking at Either an Andy forrest turbo hybrid or get in touch with Turbo Dynamics ( good company ) built my current stage 3 hybrid for fez RS, Bigger injectors and Fuel pump will be needed as well.
I would and this is purely down to my preference get a multi stage boost controller and
have 3 maps put on it, Race obviously most power, Town some boost, and eco next to no boost.
Cams performance in Blackburn got this from standard internals
Brian Coward (STi Type UK) 490.6 bhp 407.8 lb/ft
If you check out this months Jap perf car mag there is the RA developments classic which may give some food for thought
http://www.ramotorsport.co.uk/Product/Category/QD20100622015735
- there is also my personal muse the original Gobstopper by RCM
http://www.rogerclarkmotorsport.co.uk/gobstopper/official/index.htm