Hood Scoop

Lsocee, do your string test. PLEASE.
The hood "scoop" is in a Low pressure area of the hood. Open or not, it would not be "functionall". IF, it could be made to be, it would have to be in an area of the hood, or large enough, to be in air that is going to flow INTO it. Take, for example, the WRX. Its scoop is large, and sticks up much higher than the Tacomas. The deisgn of the hood alows for air to go right into it. Now, For the Tacoma, the air hits the grill area, and disrupts. it swirls along the top of the hood and into the widsheild (low pressure). NOW, the hood scoop being non "functional", if there could be a benafit to it being opened up, that would mean it would be in undisrupted air flow. Since it IS non functional, that would also mean it would contribute to the vehicles frontal area, thus impedeing air flow and creating drag. FWIW, if it were to be opened to "aid" in cooling of the engine, Im not sure if this would work well either. Air enters the front of the engine at the grill area, flows around the engine, and down and under the body of the truck. This is the most earo dynamic, and cooling efficient a truck can be.

 

No it doesnt. Silver paint does that.

 

I did my string test. I'll try to figure out how to post a video later. I taped a bunch of strings all over my hood. Then I bent them all sideways and watched to see when they straightened out. The ones in the front were the first and then the ones in the center and then the side ones. It does not seem that there is a low pressure area there.

For those that don't remember what the original debate was..it was whether or not air would flow in or out if it was opened up. The debate was not whether or not it would help. Chris and I are in complete agreement that just opening up the scoop will not improve your performance in any way.

 

Im glad you did your test. Im thinking it was different than mine? I have used the water droplets on the hood on 3 different Tacomas, and I even had a friend that is an engineer for what was Garrett Aviation look over my tests, in which he concured with my findings. Im getting tempted to start looking for wind tunnels in my location.

 

Here you go. For your reading enjoyment:
http://superhachi.com/theory/downforce/
Vents and ducts serve many purposes on cars. They are used to direct air for cooling and ventilation. However, they can also be used to reduce lift and create downforce by relieving unwanted pressure differentials. Pressure differentials can occur anywhere that a fluid flow is allowed to enter an area that is difficult to exit. If this pressure differential contributes to lift, or reduces downforce, it is obviously unwanted.
One area where a large pressure differential can develop is the engine bay. The pressure differential is created in two ways. Firstly, as the air flows into the engine bay it strikes the engine, accessories, and firewall, stagnating and raising the pressure in the engine bay. The air flowing over the hood is moving quickly and is at a lower pressure, creating a pressure differential. Because the pressure below the hood is higher than above it, lift is created.
The effect is amplified by the fact that the air entering the engine bay is heated by the radiator and the engine itself. Buoyant forces (the same forces that cause a hot air baloon to rise) are created because the hot air has a lower density than the cool air above the hood. This effectively turns the hood into a hot air baloon, compounding the problem. The problem is again made worse because the engine bay is sealed on the sides and top. This allows the air only one escape path - down. The air is forced to flow down and beneath the car, increasing drag and reducing downforce. Obviously these conditions are detrimental to a car's performance.
However, simply placing a vent in the hood can help reduce the pressure differential in the engine bay, reducing the effect of these phenomena. This solution can be seen on many race cars including JGTC and DTM cars and also on very high performance road cars like the Ferrari F50, Jaguar XJ220, and Lotus Elise.
It is important to note that if the vent is placed too far back on the hood, then it may cross into the stagnation zone at the base of the windshield. If the vent is open to this high pressure area, it may actually force air into the engine bay, compounding the problem that it was installed to relieve.
However, placing the duct in this high pressure area can be used as an advantage. On older muscle cars, "induction cowls" were used to tap into this high pressure area and provide more air to the engine, making more power. For this to be most effective, the cowl should be sealed so that the air is forced into the engine and none is allowed to collect under the hood.

 

".......The reason for this is that at highway speed, the second highest location for aerodynamic air pressure is at the base of the windshield, with the highest being the leading edge of the hood. ........"

http://www.datsuns.com/Tech/aerodynamics_and_cooling.htm

This is how the slowing and accelerating of these air particles applies forces to the car:Simply put, air that is slowed down builds up high pressures, while air that is accelerated lowers pressures.High pressures on the car start at about the front suspension cross member, and run forward to the front bumper on up and over to a point about one foot aft of the front edge of the hood.From this point back to about 6 inches prior to the wipers, low pressure exists.From that point to about half way up the windshield, another high pressure area forms.From the middle of the windshield on up over the roof, a low pressure area exists. Various aerodynamic books as well as fundamentals of flight books show drawings of this pressure gradient on wings.The Z is just a complicated wing.



And this info is for a "Z" car. MUCH more aero dynamic than a Tacoma........

 

I won't argue against a "low" pressure area. This is comparatively speaking, the high pressure area will be in front of the grill, and the area over the hood will have a lower pressure, but the lower pressure is not negative.

 

True. If I said "negative" I was in error. For it to be considered "Negative", it would have to be below 0 psi. I know better, sorry.
BUT, Since High pressure exists under the hood, if the scoop was opened, air would flow OUT of it.