Another thing you have to remember, is that air pressure DROPS as velocity increases.
Imagine holding a large straw in your mouth while riding your bike. Unless you're sucking in air as quickly as you're riding, a high pressure bubble forms around the tip of the straw, and the moving air actually goes AROUND the straw, like it had a cap on it.
Or imagine air flowing into your intake tract at a high velocity because of the speed you're travelling. It may even travel slightly faster the speed of the piston. Now imagine all this air rushing in, and the intake valves close. Boom, huge pressure rise that can go no where but back out the intake.
These are a couple of the things that are nearly impossible to calculate for guys like us.