Science of ducting air
The efficiency of a water radiator or oil cooler based cooling system is governed by 3 things:
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1.The surface area of the radiator/cooler
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2.The speed of the coolant flow through the system
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3.The amount of airflow through the radiator/cooler
The efficiency of the system is measured as BTU of heat rejection per minute.
Lets deal with the water radiator first.
In my Rover, the radiator surface area is approx 28” wide by 14” high by 2.5” thick. My radiator has been custom rebuilt and has 70% more tubes than a stock radiator. Plus I am no longer using it to cool the engine oil or trans oil - this pipework has been disconnected. So it only cools the water.
The speed of the water pumped through the system is based on the ratio of the water pump pulley to the crankshaft pulley. It should be as close to 1:1 as possible, and can be checked by measuring the diameter of the 2 pulleys and dividing one into the other. Less than 1:1 means the pump is being under-run which translates to an undercooled engine; more than 1:1 and its being over-run which may lead to premature water pump bearing failure. My ratio is 1.285 (based on a crank pulley diameter of 7 1/16” (7.0625”) and a water pump pulley diameter of 5.5”.
Lastly, lets address airflow through the radiator. This also applies to the oil coolers.
The ducting design is critical. At left is a diagram of a suitable duct. The entrance slot need only be 1/6 - 1/3 the height of the radiator provided the length of the front diverging section is equal to the height of the radiator. The outlet in this picture is a converging duct from an airplane system which is not so relevant to a vehicle. The point is that air entering the front flows into a chamber with a much greater volume and this slows the airflow down and increases the static pressure.
