Never paid attention to it over the years. Just saw one on an old MP or Gasser car. Opening in the font with larger opening in the back. What's the principle behind the design?

That scoop design wasn't a big success but it did look unique and some people still run it today just because it looks period correct.

And guys would use ANYTHING the Grump used. Chevy guys Messiah.

^^^ A lot of racers were like that back then: we used to call it "trick of the week", whether it worked or better yet, something else did.

The Grump Lump, IIRC.
I think the main principle was to cover the intake & carbs & use essentially a cowl induction.
The inlet at the base wouldn't do much due to boundary layer.
The snorkle (like the Motown Missile) quickly became popular and was a better solution.

If your boat is sinking because of a hole in the bottom, drill another hole so the water gets out.

Maybe it only looks like the back is open...

Thanks for the link, but there's no reference to Jenkins using a scoop open at both ends.

How to design the scoop?
1. sealed to the carburetor or base plate (foam gasket is enough).
2. intake opening is in clean air (or the best you can get), generally way above the hood line but will vary greatly (also front to rear on the hood) based on not only the shape of the nose, but the terminal speed - air tends to go above the roof as speed goes up.
3. for big engines with high trap speed it's a puzzle: it needs a 12" hole for the 60 foot (where car speed does nothing for air intake), but only a mail slot at 200 mph, there are formulas for this at SCTA/BNI. A 100 mph car only needs a small scoop for 60 foot (but still position-critical), and even this can be smaller for top speed.
4. cross-sectional area inside the scoop behind the opening should greatly expand (10 times: 3" × 3" becomes 10" × 10") to convert the incoming air velocity to positive pressure.
5. the scoop internal volume should be really big, trying to completely stall air speed and make it passive, so it only "sees" vacuum toward the boosters.
6. some of the benefit will be intake temp reduction, don't know how to separate the 2 effects without instruments and computer.

I should add/explain that the Grump Lump I recall had a slot at the bottom in front, and was largely open at the rear.
That was very early in PS.

The scoop that started this post had about 3/4" opening in the front and probably 3" in the back. I couldn't figure out the front opening considering that the first 1" is considered dead air. The back scoop was far enough from from the windshield that no pressure would reach the rear opening. Was it just a way of preventing the air blowing over the carb tops and creating a balanced signal?

What does it do?

It wasn't a successful design. Grumpy switched to the snorkel.