Genesis engine

"Genesis" is Yamaha's marketing name for a range of innovative high performance multi-valve motorcycle engines. The flexible design of the engine allowed Yamaha to use it on a variety of configurations, from sport bikes thru gyroplanes to outboard engines.

The dohc Genesis engine has five valves per cylinder and downdraft carburetors. Yamaha adopted the 5-valve concept, using three intake valves and two exhaust valves per cylinder, because it allowed both excellent volumetric efficiency and high rpm. As designers began to appreciate the benefits of multi-valve layout, 4-valves-per-cylinder (and even 3-valves) became common. In a multivalve engine, maximum rpm is limited by the size of the largest valves: in a 3-valver, the exhaust valve is larger, and in a 4-valver, the inlet valves are larger. The significance of the five-valve engine compared to other multivalve configurations engines is that (like a 3-valver) there were more intake valves than exhaust ones; yet all valves were small and of very similar sizes and weights. There are diminishing returns: the benefits of increasing numbers of valves actually decrease after five-valves-per-cylinder.

Downdraft carburettors were adopted for improved gas flow, but, for motorcycles, a disadvantage was that the intake airbox was above the engine, taking up space from the fuel tank, rather than being sited conventionally behind the engine.

The Genesis engine first appeared on the 1984 Yamaha FZ750 and was later used on a variety of motorcycles for different kinds of markets. The design was used for parallel-twins (such as the TDM and the TRX) as well as for four-cylinder models. Both fours and twins had the cylinder block slanted forwards 45 degrees. The Genesis engine was also used in the Yamaha YZF-R1, FZX700, FZ750, and the USA-only FZ700.

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