The Story of the Oval Inlet Ducts

When we first saw the technical details of the Ducati 1098 back in 2006, one of interesting feature was the use of oval inlet ducts, rather than circular. This was technology which was passed down from the Desmosedici MotoGP race engine. At first sight it seemed counter intuitive, because everyone else was using circular inlet ducts with round butterfly valves, and also because any shape which is not a circle will have a larger surface area and therefore increased drag and heat transfer.

But there was a good reason: while it's easier and therefore cheaper to produce a circular section throttle body and inlet into the cylinder head itself, by the time the airflow has reached the valves it's not flowing in a circular shaped path. The two inlet valves are side by side, so the airflow at a point shortly before them need to split into two streams, one going to the left, the other to the right. Before that split, the gas flow in a conventional engine will need to flatten from the circular shape to an oval one, but in the Ducati it's already oval and the flow shape needs to change much less. This makes it flow more easily, so the engine gets more air and fuel mixture during the induction stroke, and power is increased.
Kawasaki also introduced oval inlets in the Kawasaki Ninja ZX-10R, and the immediate reaction was that it was done to improve gas flow just as it was in the Ducati. You don't need to look very closely though to see that on the Japanese motorcycle, the ovals were not stretched horizontally to match the inlet valves. They're vertical: the throttle butterflies are taller and narrower than usual.

The main difference between the two engines is that Ducati has plenty of room for wide inlet tracts on a V-twin, where each cylinder is far apart, but on an inline four engine, the cylinders are next to each other. Kawasaki wanted to increase the intakes' areas was demanding more air than the previous, 2010 model. But there wasn't room to get four circular throttle bodies. So instead the area has been increased for better gas flow by stretching the shape of the intakes vertically. Tag: Inlet-Ducts Oval-Inlet-Ducts Fueling Ducati Kawasaki 1098 Desmosedici ZX-10R
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