This is an old school art.  We offer a wide array of porting and polishing packages or just by the hour.  What this does is re direct the air flow both in and out of the engine via the cylinder heads, by making the port flow more efficient. On the intake side, the ports are opened up, and the areas between the intake manifold and head and blended so there is no reversion, and the transition to the valve, via the bowl, gives you a better fuel charge, when entered into the combustion chamber.  The exhaust receives the same treatment, but it get a polish, to ensure a smoother flow out if the engine.