Race Engine Technology
Issue: September/October 2011
Article: Keeping it cool
Lawrence Butcher shows how water pump design can contribute to overall engine performance and reliability Keep it cool
Most modern race engines use water for cooling, thanks to its excellent heat absorption and rejection characteristics, although in recent years there have been some exceptions to this rule, notably Porsche’s use of air cooling until the end of the 20th century.
However, even the Stuttgart giant of endurance racing saw the advantages of water cooling over other methods, and the last air-cooled Porsche engine was phased out in 1997. The earliest water-cooled internal combustion engines managed without water pumps, relying instead on thermal siphoning to circulate coolant through a radiator. While there are a number of benefits to a thermo-syphon system – no moving parts, simplicity and water circulation rate linked to engine temperature – the disadvantages far outweigh them. These problems include, but are not limited to, the fact that the header tank must be located well above the engine to achieve good circulation, and that the coolest water enters the lower end of the engine and heats up on its way to the hottest parts at the top of the engine. However, the most important drawback, especially in terms of racing applications, is a generally low rate of coolant circulation, leading to excessive heat build-up under heavy load.
It soon became clear to engineers that pumping water around the engine block was a better solution. Even so, the earliest pumps were not reliable, and Ford even opted to delete the water pump on the Model T to improve reliability and reduce costs. By the late 1920s, thermo-syphoning had all but disappeared from automobile engines, with most engines featuring a centrifugal-type water pump. From this point on, the centrifugal pump became the standard for automotive use, with the basic design remaining relatively unchanged; the mechanical pump found on many modern engines still bears a close resemblance to those found on 1930s vintage power plants. In the intervening years, pump designs have been refined in the quest for greater efficiency; however, the greatest development in recent times has been the emergence of electric water pumps. In the modern race engine the water pump is a vital component; failure can be catastrophic while improvements can lead to increased vehicle performance. This article aims to look at all the aspects of pump design and installation, and the new directions being taken by engineers in relation to increasing efficiency and performance.
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