If you’re like many others, and your most pressing issue is the need for an increase in the efficiency of your vehicle’s cooling system, then it’s your lucky day! Increase the pressure differential across your radiator, and reduce your front end lift, with simple vents and flaps.
My cooling system works fine, however with the more is better philosophy, I decided to experiment with a few different configurations and try to quantify their effects. The best configuration yielded a 24% increase in pressure differential across the radiator than the control, at the 50mph test speed.
Configuration 1: Sealed hood, no vents.
This test is representative of what you’d see with your stock hood. For the purpose of this test, it served as a control, a baseline to which the other configurations were compared. I blocked off my existing vents as shown below. An early indication that the vents work is that the paper I used to block off the vents lifted in the back and started flapping around shortly after reaching my test speed, which was 50mph. That suggests that the pressure under the hood was greater than the pressure on the top side, at least in that region. Maybe that’s why I put my vents there.
The pressure differential across the radiator was .55 in H2O.
Don’t be deceived, my car isn’t drinking from a crazy straw. The tube in the picture samples the air pressure in front of the radiator.
Configuration 2: Vented hood.
This test was performed with the vents unobstructed.
The pressure differential across the radiator was .625 in H2O.
That’s a 12.8% increase over a vent-less hood.
Configuration 3: Vented hood with flaps.
This test was performed with the vents unobstructed, and 1.5″ aluminum flaps at the leading edge of the vents. The flaps manipulate the air to produce a pressure differential of their own. The pressure forward of the flaps becomes greater and the pressure rear of them is decreased. The reduction in pressure behind the flaps helps to draw air out through the vents.
The pressure differential across the radiator was .7 in H2O.
That’s a 24.0% increase over a vent-less hood.
These increases in pressure differential across the radiator are a result of reduced pressure in the engine compartment. Less pressure in the engine compartment translates to less pressure pushing up on the hood, and consequently less lift.
The reduction in lift can be approximated by multiplying the reduction in pressure across the surface area of the hood. The listed values are for 50mph.
The reduction in lift due to the addition of the vents was ~5 pounds.
The reduction in lift due to the addition of the vents and flaps was ~10.1 pounds.
Observation: The pressure differential generated by the cooling fans on the stationary vehicle was not great enough to register on my gauge. This emphasizes the importance of not overly relying on fans, as their effect, short of using large power hungry ones, is insignificant relative to what can be achieved with a well placed radiator and proper ducting.
The following photos are to provide insight on my methods:
The high pressure reference, forward of the radiator.
The low pressure reference, rear of the radiator.
My pressure differential gauge, and the reason why I’m using inches of water as units.