The engines used in the Honda Civic models are water cooled, single overhead cam (except for the DOHC del Sol VTEC), transversely mounted, inline four cylinder power plants. These engines are an evolutionary design built upon what Honda has learned from its engines over the past two decades.
In the 1970's, Honda offered two types of engine: Compound Vortex Controlled Combustion (CVCC) and Non-CVCC engines. The non-CVCC engines have been offered in two displacements; 1170cc (1973 only), and 1237cc (1974-79). These engines were unusually advanced for their time, both the engine and the cylinder head were cast in aluminum. The cylinder head had a crossflow design, the block used sleeved cylinder liners and a main bearing girdle to add rigidity to the block and the crankshaft rode on five main bearings.
The CVCC engine is unique in that its cylinder head is equipped with three valves per cylinder, instead of the usual two. This design employs the usual intake and exhaust valves, and beside each intake valve is an auxiliary intake valve which is much smaller than its counterpart. This auxiliary intake valve has its own separate precombustion chamber (adjacent to the main chamber with a crossover passage), its own intake manifold passages and carburetor circuit.
Briefly, the CVCC engine operates as follows: at the beginning of the intake stroke, a small but very rich mixture is inducted into the precombustion chamber, while next door in the main combustion chamber, a large but very lean mixture is inducted. (A rich mixture has a high proportion of fuel in the air/fuel ratio, while a lean mixture has a low proportion of fuel.) At the end of the compression stroke, ignition occurs. The spark plug, located in the precombustion chamber, easily ignites the rich auxiliary mixture and this ignition spreads out into the main combustion chamber, where the large lean mixture is ignited. This two-stage combustion process allows the engine to operate efficiently with a much leaner overall air/fuel ratio. So, whereas the 1975 and later non-CVCC engines require a belt-driven air injection system to control pollutants, the CVCC engines accomplish this internally and gets better gas mileage to boot.
On the 1984-88 models, Honda decided to improve engine breathing by replacing the single large main intake valve with a pair of smaller ones. This allows a much greater total intake valve area than a single valve and it also permits intake valve timing to be staggered slightly. This gave Honda engineers a unique opportunity to design air swirl into the combustion process. Such swirl (turbulence in the combustion chamber) not only tends to reduce engine knock but improves combustion speed and therefore engine efficiency, especially at low speeds. These engines retain the auxiliary intake valve on the exhaust side of the head.
All of the 1988 and later Honda engines have substituted fuel injection for carburetion, and the CVCC system is no more. In the interest of good fuel efficiency, increased power and low emissions, the two intake valves were retained. Fuel injection now makes CVCC obsolete because fuel injection provides the charge directly to the port of each cylinder under greater pressure than a carburetor is capable and permits the engine to run on leaner mixtures.
Another interesting feature of Honda engines used on 1988 and later Civic series models is the use of a single camshaft-instead of the more common two camshafts-to drive sixteen valves. The single camshaft consists of eight exhaust and eight intake lobes, actuating sixteen rocker arms. The only exception to date is the del Sol VTEC, which does use two camshafts.