| cooling
Yes fins can be designed to direct heat very effectively, however they can never do so as evenly. This has implications around the exhaust port. Look at the barrel of a W/c engine and observe the bulge around the exaust port. This is designed so extra water capacity can be realised to direct heat from the exhaust port and stop it from swelling back into the bore. Water is around 20times more dense than air. To air-cool this area you need at least 20times that volume of air come in contact with the barrel. This is possible but not practical, the engine would not fit in your frame.
The other advantage of water cooling is that the cooling can be directed to exactly where it is needed (as per exhaust port). Air cooling introduces more variables, such as air velocity, intereference and ambient temperature none of which can be controlled.
Secondly, air cooling it reactionary. To illustrate: you wind the throttle wide open at the beginning of the straight. The straight lasts 3 seconds. In this time, the inner cylinder temperature has spiked, but it may be another three seconds befre this heat soaks throught to the finns and is dissipated. In this 6-seconds, the exhaust port has swelled, puting pressure on the piston and sucking power. This is made worse if you are slip-streaming another rider. In a water cooled machine, there is a supply of cooled water lasting up to half a lap, and so cylinder temperature does not fluctuate as wildly.
It all comes down to reliability. Aircooled motors will produce similar peak power to water-cooled given optimum conditions. However engine life will be significantly less (formula A motor- 1 hour) compared to a water cooled engine (Rotax- 40 hours).
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Trying to get more people to pocket bike events held around Tasmania
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