probably the most asked question on the internet, do some googling on "zetec turbo" and "zetec tuning"

i've had zetecs N/A tuned, supercharged, and turbo'd and the turbo is by far the best.

with N/A tuned motors you have to be driving them at high revs for the fun.

some people have done shit turbo conversions on the standard ecu and using the wrong type of turbo, no intercooler etc - and then say its crap and wonder why the bottom end explodes.

they can take 280-300bhp with good tuning and breathers, best to have ARP rod bolts and dont take the revs above 6500rpm. revs will kill an engine as much as bhp.

its easier to just drop a FRS engine in though.

and look at the supercharger kits for the focus zetec from USA (powerworks and jackson racing)