Porting intake

You'll see some gain, but not a whole lot without addressing the heads as well. The majority of the gains you're going to see are from porting the lower intake. To properly do this, you'll need to add material to the lower runners before you start cutting, in order to straiten them.

Check out this article written by tmoss to give you a better idea as to how you should approach it. He seems to be out resident expert with regards to modification of the stock lower intake.
http://www.tmossporting.com/tabid/3104/Default.aspx

If you've got any further questions on the subject, you might want to consider PM'ing him directly, as tmoss is a member here.