Catalytic-converter technology is similar throughout the auto industry. The difference in Subaru technology lies in the placement and function of the catalytic converter.
Turbocharged models pose specific problems. "Catalytic converters need heat to function effectively," explains Masanori Sasaki. "Positioning the catalytic converter near the engine allows hot exhaust to pass through it. However, the engine compartment is small. So rather than installing one large catalytic converter, we arranged two or three small ones. Then we achieved a balance between the heat of the exhaust gas and resistance to the exhaust flow."
The turbocharged engine in the Impreza WRX has a low-restriction metal catalytic converter located in the exhaust-gas flow before the turbocharger. Subaru was the first manufacturer in the world with this design.
"Arranging any device in front of the turbine, which revolves extremely fast, involves a remote chance that the turbine could be destroyed, so development was difficult," states Masanori Sasaki. "However, precise design and elaborate tests made it possible.
"Moreover, metal catalytic converters are about 10 times more expensive than ceramic ones. But if we can achieve both the driving pleasure brought about by turbo engines and clean exhaust gas by adopting a metal catalytic converter, the effort is worthwhile.
"Catalytic-converter technology not only provides enjoyable driving performance, it protects the earth's environment. That, in turn, safeguards human life. We want to leave a clean environment for our children and grandchildren."
More information about Subaru emissions control can be found at Controlling Emissions - Part One.
Shielding the exhaust system between the engine and the catalytic converter helps the system to retain heat, which enables the catalytic converter to reach operating temperatures quickly.