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Pre-VTEC Oddity - Editorial

Many manufacturers considered stratified-charge technology, but only Honda successfully implemented it.

Aaron Bonk
May 24, 2011

Roughly two decades before VTEC, low-emissions pioneer Honda began experimenting with valve manipulation for the sake of lower emissions. Relatively new to automotive manufacturing at that time, the Japanese carmaker rejected the idea of catalytic converters, and instead believed its stratified-charge CVCC (Compound Vortex Controlled Combustion) engine configuration was the answer to low emissions. Stratified-charge engines that inject fuel into the cylinders before ignition were nothing newthey dated back to the early 1900s. The design reduces combustion temperatures and detonation, improves cycle efficiency, reduces heat loss, and lowers pumping losses. It doesn’t do much for power but, then again, that wasn’t Honda’s intention 35 years ago. Although CVCC engines were used by the brand for more than a decade among their various platforms (Civic, Prelude, etc.), today we file them up alongside such seldom used and outdated technologies like ATTS (Active Torque Transfer System) and 4WS (4-Wheel Steering).

Htup_1106_01_o+pre vtec oddity+aaron bonk Photo 2/2   |   Pre-VTEC Oddity - Editorial

Developed in 1968 and released just four years later, Honda’s CVCC success came at a time when fuel costs peaked and the United States’ Clean Air Act provisions forced automakers to consider alternative engine options. Many manufacturers considered stratified-charge technology, but only Honda successfully implemented it. The results were better gas mileage and improved emissions when compared to conventional engines of similar output, even those using catalytic converters. The new technology, which competitors hailing from Detroit labeled as unpractical and unreliable, helped boost Honda’s U.S. market share to unprecedented levels, arguably positioning the company for its later compact car domination.

Introduced to North America in 1975 under the guise of the Honda Civic, the CVCC engine operates similarly to a conventional, four-stroke, internal combustion engine save for a small auxiliary combustion chamber positioned around each spark plug and a small auxiliary intake valve paired with each cylinder. (Think: a combustion chamber inside of a combustion chamber.) During the intake stroke, the three-barrel carburetor injects a relatively rich air/fuel mixture (about five percent of the charge) past its auxiliary barrel into the auxiliary combustion chamber. A leaner air/fuel mixture (about 95-percent of the charge) is then injected into the cylinder that, when later combined with the first charge, still results in a relatively lean mixture. When the spark plug fires, the rich mixture ignites quickly, like any rich mixture would, which then ignites the lean mixture easier than expected, creating a swirl effect. The burn is slow, allowing time for more complete combustion, and results in less carbon-monoxide as well as fewer hydrocarbons and nitrogen-oxides, which leads to cleaner emissions but less horsepower ... by 1975’s standards anyways.

Honda’s unique combustion chamber shape and separate rich and lean intake charges created the vortex effect its engine designers were looking for. Later designs sold outside of North America incorporated more refined carburetors, even fuel injection, just before the CVCC’s demise. Interestingly enough, Honda completed its first 100 CVCC engines prior to the Civics they were destined for. As such, test engines were installed in Nissan Sunny bodies (Honda had yet to produce any car large enough to accept the CVCC engine) and sent it to the chassis dyno for further analysis. Even Toyota, Isuzu, and once-doubting U.S. automakers joined in, eventually licensing the technology from Honda for their own use. In a 1973 U.S. Environmental Protection Agency hearing, the group looked to Honda, one of only two OEMs able to meet the federal organization’s new emissions guidelines, asking the company if it could potentially supply engines to domestic automakers like General Motors should they not be able to meet soon-to-be-implemented regulations. Of course, that never happened, and instead, emissions regulations were postponed two more years, giving the domestics time to play catch-up.

CVCC technology has stood the test of time but is all but forgotten among today’s Hondaphiles even though it was officially recognized among Japan’s Mechanical Engineering Heritage in 2007. Let’s not forget the things that have made Honda great as we continue to look ahead toward the things that’ll move the company forward, lest one day we just might have this same conversation about a little something called VTEC.

By Aaron Bonk
413 Articles

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