Why is ther no formula to figure out port volume?

(To the OP) If you look at the cross-section of an intake or exhaust port you will see that it's not a very simple shape. You could make a port that is 135 cc's, but one that is shaped like a cube will flow differently than one shaped more like a smoothed funnel.

BJR, not that I really disagree with you or anything, but quite a few people recommend enlarging the intake valve on the 302's in addition to porting (of both the intake and exhaust ports) as opposed to enlarging the exhaust valve. Look at the intake:exhaust valve size ratio on an 'X' head; they too have 1.60" exhaust valves but they also have 2.02" intakes and they work great. With a good split-pattern cam, wouldn't the engine benefit more from a larger intake valve (say 1.88") than a larger exhaust valve, especially if the exhaust ports are already worked a little bit?