this is easy to answer as it’s a basic car aero discussion. Do you know why NASCAR had an opening at the base of the windshield for filling the airbox? It’s because that’s a high pressure area and also compared to under the hood. Meaning air would flow in reverse.



A lot of things opposite of most people’s intuition so it takes a lot of studying aerodynamics. Removing the seal would increase front lift.

 

So would a cowl hood also increase lift?

 

Ever hear of Cowl Induction?

Anyway the cowl itself is perhaps producing a little bit of lift as the air acclerating over the hump increases negative pressure (not too bad a place to put a vent like some of the C3's have done), but it's the windshield intersection should be your focus, not the cowl itself. That area is not doing what you think it's doing. Take a look at a spoiler in the rear... air sees this change in angle the same as a windshield. What if you put a big vent at the base, would it increase downforce or decrease downforce? Is the air pressure high where the spoiler meets the decklid?

 

I kinda get it. I think my issue is the massive amount of opinions on the subject. Even if you type into Google "does a cowl hood reduce downforce" Google AI says "Yes" and then gives a long list of reasons as to why. But then you go on Facebook groups that focus on autoX they say otherwise. As far as your questions at the end of your post "What if you put a big vent at the base, would it increase downforce or decrease downforce? Is the air pressure high where the spoiler meets the decklid?" I have no idea what it would do to downforce or if the pressure is high or low. I'm very ignorant to aerodynamics as a whole. That's why I asked the question about the cowl seal. I was just trying to understand it a little better.

But even if I don't really get it thank you for taking the time to explain it.

 

Yeah it’s a very interesting subject… with regard to placement of the vents… we haven’t even talked about how the vents in the rear would likely reduce the huge lift gradient on the top of the car.

think of it as high pressure on top compared to the bottom, means more downforce… low pressure up on top compared to the bottom means more lift.

If you put a huge cowl on the front, the leading edge transition, especially if it has a smooth scalloped shape, may provide an added high pressure area.

the top of the cowl, or the top of the hood, or the top of the roof, has a rounded area that really pumps a lot of lift or suction from the airflow. Placing a vent or air exhaust/extraction on any of these areas will usually reduce the lift… generally speaking. So you can design a cowl that adds pressure at the front, and exhausts pressure on top, and inducts pressure for the engine intake at the end, this can all be good.

at the back end of the hood or cowl, air pacs into the scallop at the windshield and creates high pressure that is probably just a fraction of the lift that the hood creates, but because it’s high, it’s a perfect place for induction, and poor place for extraction (the original idea presented).

a less rounded nose where the headlights start would help with downforce, but would not look very good. Lot of the late model modifieds do this. Soon as you start making it round it produces lift like the top of a wing on a 747 that lifts up 500 tons of weight at 180mph