Porting heads?

How is it done? How does it help?

In simple terms: Its tricky.

Its where you take the intake the intake and exhuast ports on the head and reshape them for optimum flow and maximum volocity. Alot of people tend to just hog out the ports (seen some people make the entire runner the size of the valve), and this generally makes a very sluggish motor untill it reaches high rpms because the lack of volocity to help fill the cylinders with air/fuel. But on the other hand if you make it too restrictive it will not flow well enough. A flow bench is a common term thrown around in head porting, its a machine that measures how much air can flow though a head at given valve lift, but it takes alot more than that to make the most power, as numbers can lye. You need feedback from heads that have been done, how they react, and at what rpm they do what at. Its not a given science, differnt engine designs act differntly. Unless you have time and facities to try things, test them, look at the results, test more, and repeat untill your blue in the face its best to find what works for your motor that someone else has done and replicate that. Most offen your best choice is to simply apply known proven methodes such as removeing the casting marks, polishing the exhaust side, and port matching the intake side, and leave it at that.