RESERVOIRS. The size of the reservoir is of prime importance to the efficiency of the water-based IC. Consider that most applications of boost will last only a few seconds—say, 15 as a high average. Then it is reasonable to be sure in this interval that any given piece of water will not see the IC unit twice. A pump capability of 10 gallons per minute will move 2.5 gallons in 15 seconds; thus, the ideal size of the reservoir here is 2.5 gallons. Unreasonably large, obviously, but the point is made that the bigger the reservoir, the greater the time until the water takes its second lap through the IC. It is not too difficult to see that as a larger reservoir is used, the need for a front cooler decreases. Consider that the greater the mass of water, the greater the thermal inertia.

FRONT COOLER. The front cooler is the least important part of the IC system, as it is doing most of its work when the vehicle is not operating under boost. At the start of a boost run, the entire system will be at approximately ambient temperature. As boost rises, heating the water in the main core, this heated water must get to the front core before it has any temperature difference with which to drive the heat out. This time delay can be as long as 7 or 8 seconds, depending on the size of the reservoir. That amount of time is typical of a boost application. It is clear, then, that the front cooler will do most of its work after the boost run. Since the temperature difference between the water and the front core is small compared to the temperature difference between the boost charge and the water, the time required to cool the water down is much greater than the time required to heat it up. This is another reason for running the water pumps all the time. The front core does not need to be as big as it may seem at first glance, because the relative cfm rates through the two cores will usually be heavily biased toward the front cooler. For example, a forward velocity of just 60 mph could potentially put 5280 cfm through a cooler of 1 square foot area. Surely it is another case of bigger is better, but not really enough better to get carried away with huge front coolers.

WATER PUMPS. Easily the most usable pumps are 12-volt marine bilge pumps. These can be ganged in series or parallel, depending on pressure and flow capability of the pumps. The fundamental should not be overlooked that the more water circulated, the greater the IC efficiency. Consider a water flow rate of 10 gallons per minute a reasonable minimum. There is a trade-off in pump life versus IC efficiency if the pumps are required to run all the time. With performance the focus of all this work, the answer should be that the pumps run continuously. If the pumps run continuously, the interesting thing happens that when off boost, the intake air will be cooling the water in the IC.
Wiring the pumps to a switched 12-volt source will permit an audible inspection of their function every time the ignition is turned on. The pumps should be mounted as the low points of the IC system, so that they will always be primed and thus preclude the chance of their running dry.