if you were to take you head off (the engines not your own) and remove the cylinder you would see 3 holes in it (using 3 port design as example) 2 holes would be across from each other and these are the intake ports, the one in the center is the exhaust port. a more agressive engine can have several intake ports arranged in various shapes and sizes. the engine builder uses these to try to make the engine more efficiant for whatever vehicle/use the engine will see. this a simple question,and this is the simplest answer i can think of, its like this the more air and fuel you can make the engine burn the more power you will get. if you are racing check your rules some classes may require you to run only 3 ports. and one more thing having only three ports does not mean you have a slower motor some of the most popular engines sold are 3 port ,there are so many other things that affect engine performance, crankshaft design, carburator , and the shape of the connecting rod (knife edging), compression, and your nitro %. keep searching on google and you should be able to find several articles on porting . good luck,kman