I've seen a lot of mixed opinions on whether the formula bulge generates positive or negative pressure at the opening, so I wanted to settle it. Yes, the air speeds up over the top of the bumper and hood generating a low pressure zone over the bulk of it, BUT when that fast moving air slams into the base of the windshield it compresses into a high pressure zone (or at least higher than the pressure inside your engine bay), which pushes air into the opening. That's why GM made it a functional intake on some trims. Anecdotally I would also guess it generates a vortex behind the bulge which helps prevent viscous shear forces from pulling air out of the opening.
To prove this, here is a cfd I ran. Yes it's a Camaro because I ran it for a different project but it's close enough to show the high pressure zone at the base of the windshield.
I also used the old school technique of taping a bunch of string to my car. The string follows the path of the air so you can actually see the air getting sucked into it. Here's a link to a slow motion video of it on my channel too. https://youtu.be/nU0nbamwWYY

 

Interesting to see data. My own anecdotal observations suggested it pulled air in too. When my car was tbi, I had the intake hooked up and leaves would get sucked up to the screen fairly regularly in Fall.

 

I don’t think the turbo hood was originally designed to pull air from the base of the hood/windshield area. The hood was designed to provide more room for the taller carb/turbo/manifold assembly on the 301T. That’s why it’s offset to the driver’s side. When the decision was made to go corporate SBC for all V8 engines in ‘82, the scoop was opened up in the back to provide some level of air-induction for the N/A SBC on the performance models.

 

That is why the 1970 Chevelle SS cars had cowl induction at the back of the hood due to the high pressure area created there Same story for Nascar.

 

Is the duct on the underside of the hood installed and functioning? I don't see the engine mentioned in your post or in your profile. Carb, TBI?

 

It's actually a 92 Camaro that I swapped the front end of an 84 firebird onto. The firebird I pulled everything off of had a crossfire intake and I have a TBI so the duct doesn't fit, so for now it's just open to the engine bay.

 

Thanks for posting this! I've always hoped someone ran some CFD on these cars. This is indeed helpful. Are the profile images showing airflow down the centerline of the car?

 

Yep, a plane right through the middle if I'm remembering correctly.