The Subaru PZEV or Partial Zero Emission Vehicle engine technology enables Subaru’s Boxer engines to emit significantly less tailpipe emissions while running on regular unleaded gasoline. The movement toward PZEV engines began in 2014 when the U.S. Environmental Protection Agency (EPA) published its Tier 3 Motor Vehicle and Fuel Standards for emissions. The California Air Resources Board (CARB) was the first to coin the Partial Zero Emission Vehicle or PZEV moniker in 1998 to encourage auto and engine manufacturers to implement new technologies to curb harmful emissions.
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According to Subaru Canada, vehicles with the PZEV badge are “the cleanest-running gas-powered” vehicles available. PZEV cars have engines that “meet the Super Ultra Low Emissions Vehicle (SULEV) tailpipe standard and have zero evaporative emissions” while offering performance comparable to hybrids, diesel cars, and non-PZEV vehicles. Subaru vehicles classified as PZEV include the Crosstrek, Impreza, Outback, and Forester.
What makes PZEV different from a standard combustion engine?
Subaru PZEV vehicles have engines with modified smog-reducing components. They have larger catalytic converters with almost twice the contact area of a regular cat, enabling them to filter more smog. Meanwhile, it has a dual-filtration air-intake system with charcoal canisters to absorb hydrocarbon emissions. Conventional non-PZEV vehicles emit unburned fumes through the air intake upon turning the engine off. The dual air-intake filters prevent those fumes from escaping into the air.
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Moreover, Subaru PZEV cars have custom fuel injectors with tips that close tighter to prevent fuel leaking into the intake manifold, which keeps harmful emissions from escaping. The final mod is an optimized engine control module (ECM) that delays the ignition timing during cold starts. The process raises the temperature of the exhaust gasses, which in turn heats the catalytic converter quicker to reduce tailpipe emissions.
Sustainable America claims the PZEV engine mods contribute to cleaner air by capturing hydrocarbons, carbon monoxide, nitric oxide, and other non-methane organic gasses that would otherwise escape from a non-PZEV car. However, PZEV vehicles still emit CO2 fumes despite spewing 90% less smog-inducing and acid rain-producing emissions. The ultimate goal is to reach ZEV or zero-emission vehicle status, but PZEV cars are a step in the right direction.
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