[Christ]

Someone please do a test for me:

Turn on a faucet at 6 gallons per hour.

Put a funnel under it that can only flow around 3 gallons per hour.

Measure the "wasted" water that doesn't make it through the funnel.

That will prove that those holes aren't what they're cracked up to be. Keep the air from getting in there to begin with, you'll be better off for it. If you look at those holes, they represent less than half the surface area of the bumper. If the bumper in theory is filled with air, those holes are only relieving some of the pressure build up, causing (probably) more harm than good.

Imagine what happens when you force a fluid through a hole at pressure that isn't tapered, as well. The coanda effect says that the fluid (air) will attempt to adhere to the object it's being forced through, which means that it will expand very quickly as it leaves the hole, possibly causing more drag.

So first, you're pressurizing it, then, you're allowing it to expand. Sounds like a huge waste of energy to me. Why not save your grief, build a small belly pan, or just cut the bumper and add vertical stabilizers?