Don't think every tuner who ports head puts each one on a flow bench ! A friend of mine who helps with my engines ports my heads (lets me cut the material out and he shapes/finishes the ports) and i've had good dyno proven results. He picked it up from someone who really knows what they're doing years ago and has just progressed through doing lots of them and dynoing engine's (he's also flow tested some i believe). It is a bit of a black art i believe, in that people who port heads just know what works and what doesn't and don't have to put every one on a flow bench to prove it. The chap who does mine merely does it as a hobby and for friends, and has done various heads for some big power cossie motors, over 5 years ago now he ported the head of one that made 630bhp so it can most definately be done at home in your garage! In fairness though he mainly does cossie/cvh heads as he really knows his stuff on these, every engine will require different porting techniques to get results so it's not just a matter of taking material out to get bhp, so if you're just looking to do zetec heads you should be able to research what works on them. As said though you'll probably spend alot of time and development work to get anything like the results of a proven head porter.....if you're happy with that then give it a go for sure mate, ideally you need someone to point you in the right direction and give you some hands on advice