I found a good calculator for all your guys out there interested in seeing the difference between a large port and a small port in terms of air velocity.

http://www.engineering.com/calculators/airflow.htm

You can play with it and see that a smaller port that flows the same air as a larger port yeilds much greater velocity.

 

By physics, it makes perfect sense. Move the same amount of anything thru a smaller opening as compared to a larger one, the stuff moving thru the smaller has to be going faster.

However this isnt the end all be all to performance... higher velocity ports are good for lower engine speeds. As air speed picks up thru the port, there can be issues of too high velocity causing flow to choke. The boundary layer of air that forms on the surface of the port can start to separate as air speed increases to a certain point, and thus no more air flow can get into the cylinder. This hurts power.

So in some cases a port thats larger and flows less on a flow bench may actually make higher power at higher rpms because its air speeds are within acceptable levels/tolerances.