I've driven a mk5 zetec s turbo running 6-7psi and it was fairly quick, but any more boost and the engine would quickly kill itself, I would advise either building the engine youve got properly, ie low compression, forged pistons etc etc, or swapping it to a 2.0 zetec (which requires all new mounts, driveshafts, wiring loom etc etc) with the appropriate mappable ecu, ie megasquirt or omex, neither of which come cheap!

Good luck to you.