Let me put this in an honest a fashion as i can.....
the 2.0 8v engine is UTTER TURD. It will NEVER EVER EVER produce decent power without throwing an awful lot of money at it. and even then all you will end up with is about 150 ish bhp at a push. and in a big heavy car like a mk4, that is simply not going to be enough.
standard 150bhp 1.8 Turbos are slow as standard, even the 180bhp fail to set the world alight, so seriously, GIVE UP.
To get 150ish bhp out of the 2.0 8v will require the following:
Seriously ported and polished head, knife edged ports, "bulleted" valve guides, double valve springs and sodium filled (or similar) valves.
High lift Cam and vernier pulley.
Your looking about £1k for the required level/standard of work on this head.
Bottom end:
lightened and Balanced Crank
lightened and Balanced Pistons
lightened and Balanced uprated rods
uprated wrist pins
lightened and Balanced flywheel
Again your probably looking at close to 1k for this to the required standard.
Stainless exhaust manifold, Racing CAT and full straight through to backbox system
approx 700 for a miltek system.
BMC CDA induction kit with cold air feed
£300
Uprated Oil Cooler
£200
ECU remap to increase fuelling
£400
Quite probably larger injectors too, or new nozzles at the least
£2-500
so now you've spent around 3-4k on tuning the 2.0 8v and you will still only have 150bhp ish...
you could buy the 20vT engine for approx 800, and even if a garage fit and remap it for you you'll be looking at £1200ish, so £2k in total for approx 185bhp......
I know what id do......