[NoDOHC]

I think you understand this issue better than most already.

The purpose of port matching is to avoid any steps in the intake runners (where the ports do not match) which impede flow.

There are various factors that can impede flow, one of which is a step in the pipe.

Bad flow results in a loss of power (pressure drop in the intake runners will reduce the pressure in the chamber when the intake port closes, thus decreasing the volumetric efficiency of the engine)

The air must flow at a certain velocity in the pipe in order to acheive a certain flow rate. Losses are related to velocity (slightly greater than the 2nd power). Larger diameter pipe will result in a lower velocity (fewer losses).

The effective diameter is what I call the center portion of the intake runner that is able to carry air (not effected by the boundary layer). The boundary area is determined by surface roughness of the material. Polishing the runners will decrease the boundary layer, increasing the effective diameter of the runner. Bear in mind that increasing the size of the runner has it's own implications.

Larger runners will help high end and hurt low end (due to fuel mixing problems and lack of energy for inertial or resonance tuning).

Please remember that with any intake-injected engine, it is not all about air flow, but fuel mixing and mixture distribution are equally important. On a DI engine, it is only air, so make it flow as well as you can.

On no account should the intake port be larger in cross-sectional area than the runner (unless this is a track-only engine). This will result in a poor low end performance and excessive fuel consumption as some of the fuel will fall out of suspension in the runner as it expands.

If a runner diameter can't be maintained constant, it should decrease area as it goes toward the engine as this will keep the fuel in suspension.

I wish I could explain this simply, maybe Vex can help me out:

Any step in the wall of the pipe disturbs the flow of the air, so does any change in cross-sectional area (as it requires a change in the velocity of the gas). Turns also create losses.

Basically, any time the air changes velocity (magnitude or direction) it requires energy to do so. This energy is absorbed from the incoming air as a pressure drop in the intake runner.

To make a long story short, what you say is true. If you gasket-match the intake manifold to the block without addressing the cross sectional ares of the intake runners or the block, it would probably have been better to have left it alone. If you gasket-match the intake and then make sure that the runners also match the cross-sectional ares of the intake manifold gaskets, you should have a very good flowing engine.

It is completely acceptable to polish the exhaust ports to a mirror-like finish. This will do no harm to the engine. It will have two effects:

Nominally better heat reflection (less exhaust heat absorbed by the inserts).
Slightly louder exhaust note (less sound energy absorbes by the exhaust ports).

Exhaust ports should increase in size as they leave the engine. sharp steps are a no-no, but the gas is expanding and cooling, so it will need more cross-sectional area as it moves away from the port.

My friend who taught me to port always said "If you think bigger is better, leave the exhaust port alone."

I hope this helps. It helped me when it was explained to me.