Back in the day (1973) I was pretty good friends with the parts manager at the local Pontiac dealership. I also owned a 1969 non ram air GTO. I was able to purchase a pan and air cleaner for under $40 bucks that someone had ordered and never picked it up. I opened the scoops and installed it, there was a definite addition of power with it on the car per butt dyno.
I never raced on a dragstrip, so times aren't there to back it up. Doubtful Pontiac engineers went to all the trouble to tool up for something that had no effect on engine power.
Later on I tried cowl induction on my 67 GTO clone dirt car and it also worked better taking cool air from the base of the windshield. The drawback is that after a race it worked so well that I had a bunch of fine gravel/sand inside of the air cleaner base that was stopped by the air filter element. I decided not to continue using the cowl induction setup because of the amount of dirt ending up in the air cleaner base.
Chevy had more benefit from the cowl induction actually having tapped into the base of the cowl and a high pressure area than Pontiac did with their forward facing boundary layer hood scoops. Seeing that the finer dirt was ending up in my air cleaner shows that there was enough positive pressure to push dirt through the ducting, and into the air cleaner. The vents that push air into the interior of the car also show that at 60 MPH there is a definite positive pressure area near the base of the windshield.
If I wanted the best functioning system,the aftermarket system that has ducts in the front of the car near the bumper, or a cowl induction system similar to what NASCAR has used in the past (taking air from the area behind the cowl vents under the grille at the base of the windshield) are the most effective systems in my opinion from my experience.
One other thing is with open scoops I never had any problems driving the car in the rain (I lived in Erie PA at the time, and they don't call it Deary Erie because the sun shines all the time
) If memory serves me, there are small drain holes in the lowest points in the air cleaner assembly for water that would make it's way into the air cleaner to drain from.