Subaru engine components and systems are designed to keep emissions at low levels.

A Subaru vehicle reduces harmful emissions by burning fuel as efficiently as possible. Here are some of the components and systems that contribute2:

  • Electronic control of engine and transmission functions by microcomputer fine-tunes engine components to the variables of intake air and exhaust composition
  • Electronic Throttle Control precisely interprets driver input
  • Direct ignition eliminates wiring and enhances firing precision
  • Mass air, anti-knock, and other engine sensors contribute to precise operation while safeguarding engine components
  • Variable intake- and exhaust-valve timing enables a wider range of engine power and improved combustion
  • Intake systems promote the thorough mixture of air and fuel
  • Sequential multi-port fuel injection more precisely regulates fuel flow
  • Four valves per cylinder promote improved breathing to maximize combustion
  • Centrally located spark plugs in the cylinder heads help to maximize combustion
  • Reduced-friction designs of valve springs, piston rings, oil pumps, and other engine components promote power development and operating efficiency
  • Catalytic converters and O2 sensors help reduce harmful emissions in the exhaust system




As exhaust gases leave the engine through the exhaust system, catalytic converters help to reduce CO, HC, and NOx emissions. Converters look like small mufflers from the outside, but contain a ceramic honeycomb to which platinum, palladium, and/or rhodium have been fixed. The converter catalyzes the change from CO, HC, and NOx to CO2.


Catalytic converters don’t function properly until heated to approximately 600 degrees Fahrenheit. So when the vehicle is started, its control modules increase idle speed and raise shift points to help the engine warm up quicker.




Subaru engines evolve from year to year. Small and large tweaks and modifications promote higher efficiency and improve emissions control. These measures provide a sharp contrast to the capabilities of engines in vehicles manufactured just a few decades ago.


This article is part of a series that will address the Subaru R1e electric cars now undergoing testing (see the Subaru News section) and Subaru PZEV engines. Watch for these stories in future issues of Drive.


1 For more about the four-stroke cycle, see “Active Valve Control System (AVCS) – Timing Is Everything” in Winter 2005 Drive.
2 Not all are available on all models.



Cautions for State Emission Testing


If your state requires emission testing, please be aware that full-time 4WD and AWD Subaru models must never be tested on a two-wheel dynamometer. Serious transmission damage could result.



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