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5
Higher Compression Ratios

One way to improve performance and fuel economy is to increase the compression ratio inside the engine. The compression ratio refers to the amount of fuel and air squeezed into the combustion chamber. When this ratio is higher, it uses fuel more efficiently.

Mazda is using this approach to its latest generation of vehicles, both diesel- and gasoline-powered. The SKYACTIV-G gasoline engine, for example, uses a 13:1 compression ratio in North America, where the norm is 10:1. SKYACTIV-G vehicles in Europe have a 14:1 ratio, since more people in Europe use high-octane gasoline regularly.

The problem with higher compression ratios is usually a knocking sound in the engine, which occurs when temperature and pressure are too high in the chamber and the air and fuel mixture ignites too early. Higher octane gas on its own can solve some of this problem, but Mazda has developed a longer exhaust manifold that reduces the temperature and the chance of engine knock. The SKYACTIV-G system also has a faster combustion time, which means the air-fuel mixture ignites properly before the temperature can build up and knocking begins.

All this engine technology -- as well as weight-saving materials and a new transmission -- mean 15 percent lower fuel consumption and emissions and 15 percent more torque. And increased torque translates into more driving fun.

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