If you get the exhaust too, then the air in can happen quicker and the exhaust out can happen quicker too, which is a good thing. 
Which wouldn't make a blind bit of difference as the time the valves open and shut for would still be the same, thus the volume of air entering and exiting the cylinder would still be the same as it would were it on a std panel and std exhaust.
Change the cams to make a noticable difference.
