Remember that the valve train is very similar to the 750cc OW-01 motor and that enjoyed valve train stability all the way to 13,500rpm and more . Yamaha ’ s Genesis motors seem to have an already generous amount of valve / time area in their design . “ The five-valve design was eventually discarded in 2005 in Yamaha ’ s big sport bikes . In reality , it offered no significant flow / burn advantages over a good four-valve design . The marketing department at Yamaha held on to the five-valve design long after the engineering department wanted it gone . In fact , in a standard head , one of the three intake valves does very little work getting air / fuel into the combustion chamber . This is particularly true of cylinders one and four . The standard combustion chamber , whose shape is determined by the valve layout , is suboptimal compared to a good four-valve chamber . This results in a relatively slow burning chamber . In fact , the 750cc OW-01 standard head requires a staggering 45 degrees of spark advance to get peak torque . A 750cc Kawasaki of the same era requires nearly 10-degrees less advance to achieve its peak torque figure
because it has a better combustion chamber profile that enables a faster burn . “ The Yamaha five-valve chamber is like a flat pancake shape that also presents a very high surface area to volume ratio . This also contributes to thermal losses which subtract from the useful work energy that the motor produces . This becomes waste heat into the exhaust and , more importantly , the cooling system . The higher advance figure also increases pumping losses in the motor . Some of these problems were solved in this race bike as evidenced by the fact it uses a standard YZF750 radiator . When everything is all good , the engine temperature remains in the high 70 to low 80 degree range . “ The five-valve motor did offer a brief rpm ceiling advantage by way of a lighter maximum valve weight . In a four-valve motor , the intake valves are the bigger . In the five-valve Genesis series , the intake valves are the lightest . For a short period of time Yamaha enjoyed an rpm advantage over its four-cylinder rivals by virtue of its lighter valves , and subsequently lighter valve springs . However , the full advantage of the
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