In reply to Box4VIR :
It will be clean but comparatively slow moving air. Partly because of the sharp 90 degree turn it has to take, and partly because it exits near the front of your hood where there's similarly clean and fast airflow. I don't see an added winglet giving you that much more downforce than what you'll already get from your current setup.
Instead I would recommend installing a wicker / gurney flap in front of the opening in the hood as wvumtnbkr suggested. Make it tall and almost perpendicular to the ground. You want to artificially create a low pressure area directly above the hood opening to encourage the air to come through. It will look a bit odd but it will generate a lot of downforce.
Fortunately I was able to get out an run at VIR before all of this Coronavirus nonsense and test out the new hood. It was freezing cold but it definitely had more front grip, hard to tell with the temperature but I think in warmer weather I'm going to be struggling on the straight aways. Also take a look at the picture below the air coming through the front scoop is putting enough pressure on the hood to push it back an inch or so and buckle it in the middle. I either need to add some flaps(as suggested) to direct the air or change the whole design to pull air from under the car through a splitter/diffuser. What are your thoughts.
here's a few of the first first pass
potentially you've got enough air coming in the front, and a 'tight' enough turn that it's providing enough pressure on the 'aft' side of your duct to cause the buckling, and it's not just the flow coming over the top. You could probably test this theory by putting a foot through the duct and pushing as much pressure on the upward slope of the back of the duct as possible. I'd have to run some numbers, but a foot pressing ~80-100#s should be that much different than the air at 100-120mph, psi-wise? If anything, it'd be a bit low?
And yes, I still think you need to close up your opening, and add a 'flap' of sorts behind your aerocatches
