In 1975, amidst increasingly more stringent emissions regulations, Honda introduced their CVCC “ED-1” engine. CVCC stands for Compound Vortex Controlled Combustion, a unique form of the stratified charge concept. Honda’s idea incorporated a third intake valve into the head of their engine that brought a very rich fuel-air mixture into a small chamber next to the spark plug. The normal, larger, intake valve allowed a leaner mixture directly into the combustion chamber. When the plug ignites the rich mixture in the extra chamber, the flame spreads outward to the combustion chamber and ignites the leaner mixture. A leaner fuel mixture generally means fewer NOx emissions but a lower power output. The use of the additional rich mixture allows easy ignition, and then the flame flows outward to the combustion chamber and ignites the remaining leaner fuel mixture, thus, making the most of the fuel available and reducing emissions at the same time.
The original CVCC used a carburetor system with two separate venturis and two separate fuel mixtures for the separate intake valves. Later, CVCC technology was adapted to other engine designs from Honda and received as many as three separate carburetors in CVCC-II form before finally becoming fuel injected in EW5 series engines of the mid 1980s – though these were only sold outside of North America. In addition, CVCC Hondas eventually received catalytic converters as well, further reducing the emissions of these cars. The system faded away at the end of the 1980s and Honda began experimenting with valves again with the introduction of VTEC. But that, of course, is another story.