Jeff, you're getting me in trouble. I don't want to start an arguement and I have the upmost respect for earringboy's engineering knowledge. Under most circumstances the air flows in the cowl not out. The air directly above the cowl is stationary and not moved by a venturi effect. It blows in as a result of the Bernoulli effect as an extension of The Law of The Conservation of Energy. That's why it's called a cowl induction hood not a cowl exhaust hood. NASCAR agrees. Air can only blow out from positive pressure under the hood or car or as hot air rising. This is while sitting still maybe while the radiator fan is blowing. Most race cars have good enough ground effects to prevent high pressure under the car. A noticeable exception was the Superbird which had fender vents to let it out. The PT's rounded nose will blow as much air around the sides as over the top and you won't be going fast enough to worry about pressure under the car.
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