Released in 1973, Honda's CVCC system, or "Controlled Vortex Combustion Chamber", was a method of getting a near-stoichiometric fuel/air mixture, increasing fuel economy, and decreasing emissions. This system was so effective that the Civic CVCC was able to pass California emissions requirements without a catalytic converter. Various Honda websites disagree on the first model year with this feature, with Honda of Canada claiming 1972, and most other Honda sites suggesting 1975. Regardless, the technology was announced in 1971, and in 1977 led the Civic CVCC to be ranked first in fuel efficiency on the EPA's new top ten list.

CVCC is a system used by honda to reduce emissions by stratifying the combustion charge. In the City turbo the throttle body appears much like a carby. However fuel is only applied through one barrel via a single injector (the throttle body has three barrels). A separate set of intake runners provides fuel to each of the CVCC valves located with a combustion prechamber. A rich mixture of fuel and air are added to the combustion prechamber which houses the spark plug. This is ignited and creates a flame front out of the prechamber. The flame front is used to ignite a lean mixture (normally hard to ignite using a spark plug) fed to the main combustion chamber via individual injectors.
Honda City Turbos and the Beginning of Mugen Motorsports, Charles Hatcher

The original Honda CVCC motor was an 1.5 liter inline four cylinder motor (or I-4) mounted transversely, and inclined forward to fifteen degrees much like Chrysler's "slant six" engines. It was a belt-driven single overhead cam (SOHC) engine. There is one intake valve on the prechamber, mounted above the main combustion chamber, and two on each main chamber, one for intake and one for exhaust; Whether this really makes the engine a 12 valve or it should be considered an eight valve design is thus debatable.

Honda Accords also used CVCC-based engines from 1976 to 1981.

Honda is not the only manufacturer to use a prechamber system to enhance combustion. Though it is fairly rare in gasoline engines, it is more common in diesels, most notably the engines made by Mercedes-Benz.

References:

  1. Webpage: Honda Insight: Hybrid gasoline-electric car. Ars Technica, 2000. (http://www.arstechnica.com/reviews/3q00/honda/insight-1.html)
  2. Webpage: Environment. Honda of Canada. (http://www.honda.ca/athondaca/environment.asp)
  3. Webpage: Honda City Turbos and the Beginning of Mugen Motorsports. Charles Hatcher.(http://asia.vtec.net/beystock/project/cityt.html)
  4. Webpage: Best Engineered Car of the 20th Century. Automotive Engineering International Online. (http://www.sae.org/automag/bestcar/08.htm)

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