The way that the "raisin bran" scoops are molded into the hood, it would only create a negative pressure if they were rear-facing, as well. Also, at very high speeds (over 150 mph), it is possible that the pressure that builds under the hood would be enough to create a net negative pressure at the hood scoops, but it is not likely. The possibility of this is why the underhood area is often vented separately on a high-speed car. Why do NASCAR racers not use scoops for air induction to the carb? Because there would be too much air then, due to the speed of the car, and the amount of air that would "stack up" in the air inlet tract. Land-speed racers often block off the majority of the cowl vent because of this, and NASCAR racecars are equipped with a removable plate in this location, to facilitate different openings for different tracks and speeds. Too much air in the inlet can actually slow the car down, due to resistance caused by the air stacked up in the inlet tract. Look at any factory system, and you will find flaps that will open up and bleed off air from the tract, to avoid this on a regular car. The Ramcharger box from the 1969-70 Coronet, and the Air Grabber box from the same vintage Belvedere line, are excellent examples of this strategy. A similar strategy exists in all factory fresh air induction systems, be it flaps, vents, or loose-fitting components. This is less prevalent in shaker or "demand" systems, because they never seem to be open long enough to over-pressurize. A lack of proper venting of excess air was inflicted upon the last rendition of the Ram Air Firebird, and has reportedly resulted in lost hoods. A system needs to be thought out carefully for maximum performance, best style, and easiest asembly and service. Studying well-scienced induction systems always helps, and there are ways to do almost anything, as long as one is willing to try. One of the easiest fresh air systems I ever did was a ram air system on my first Barracuda- a 318-powered '68. I used a 4" dryer duct, duct-taped to the air cleaner snorkel, and affixed to the radiator support under the battery tray. There is a hole in the support here, and it is open to the high-pressure area in the front of the car, behind the grille. I picked up 3 MPG, and a good 10-15 HP across the board. Simplicity is good, and creativity should be encouraged. The simple rule is this: if it scoops air from the base of the windshield, the very front of the car, or from a point at least 1" above the surface of the car, it is ram air. Everything else is just fresh air, but that is at least a step up from choking on the hot stuff under the hood.
