Road and Track - April 1974

Vol. 25, No.8

In October 1972 Mr. Soichiro Honda, founder and incumbent President of Honda Motor Company, introduced the CVCC "stratified-charge" engine and pledged solemnly that his company would offer to the public a super-low-emission car powered by CVCC at the end of 1973. This new car would meet the stringent emission requirements of 1975 for both Japan and America. On December 12, 1973 Mr. Kiyoshi Kawashima, who had now inherited the leadership of the company from Mr. Honda, announced proudly that Honda was fulfilling the promise by launching the world's first volume-produced car with a stratified-charge engine: the Civic CVCC 4-door sedan.

The Honda Civic CVCC meets the Japanese emission standards for 1975, which have been modeled after and closely follow the contents of Senator Muskie’s Clean Air Act Amendments of 1970. The Japanese standards are not statutory or mandatory yet but likely will be enacted without delay. The government now offers a temporary tax concession to cars meeting them before the official deadline, and the Civic CVCC is the fourth car qualifying for the consideration. The other three are Mazdas, two Wankel and one piston-engine models, all employing thermal reactor systems.

The Civic 4-door is also offered with a normal 1.5-liter engine in two stages of tune, for obvious commercial reasons. This version will most likely be exported to Europe, but Honda's European program has not been announced. Export to the U.S. market will begin in September of 1974, and the U.S. 4-door will have only the CVCC engine regardless of the federal government's tempering of the 1975 standards (see the Emissions table). Production of the 4-door models is building up at the modern Saitama Works, whose facade displays large CVCC letterings, from an initial 1500 cars per month to a target of 10,000 by August 1974.

Honda saw ever-tightening pollution-control legislation, especially in their most important markets (Japan and the U.S.), as early as 1960 and began its search for a low-emission power source then. The Honda Research and Development Center, known for Grand Prix motorcycles and cars and responsible for the design of all Honda products, studied-and in some cases actually developed-many alternative automotive power units as well as add-on emission-control devices for the piston engine. It was even rumored at one time that Honda had a small sedan powered by its own "teapot" gas turbine swooshing merrily about the R&D premises. But Honda concluded the gas turbine had a long way to go before it could overcome its high material cost and inherent poor combustion efficiency under light operating load. The situation appeared similar for the Stirling engine. Honda also didn't budge in the Wankel rush of a few years ago, deciding against the rotary because of its poor fuel economy. The diesel was ruled out because of its weight disadvantage and unsolved fume and particle problems. Electrics would merely transfer pollution to other sources.

By the late 1960s Honda's course was chosen: refinement of the conventional piston engine. As for the add-on device system, Honda had been and still is doubtful about longterm efficiency and durability of catalysts. To date Honda has not found materials suitable for a catalyst that would control oxides of nitrogen, or NOx, the toughest pollutant to kill. There are two basic approaches in modifying the conventional piston engine to reduce emission levels. One is a "rich approach," feeding a mixture of air and fuel richer than the ideal value of 14: 1. This dulls the engine's combustion efficiency and reduces NOx, products of hot and efficient combustion; carbon monoxide and unburned hydrocarbons spew out from the exhaust port, however, and have to be taken care of by a catalyst system or afterburner. The dreaded exhaust-gas recirculation is another way of lowering combustion efficiency, but it too brings a penalty in fuel economy. Fuel economy was an important consideration for Honda, whose forte is the small and economy-class car league, so the choice was the "lean approach," or feeding a leaner mixture to the engine, and control of the three major pollutants in the combustion process proper.

The CVCC project got under way in mid-1969; the name was to represent Compound Vortex Controlled Combustion. The finished product as offered in a Civic 4-door sedan is more like CvCC. In an early stage of development, strong turbulence and vortex effects were sought in the combustion chamber as an effective means for better combustion, but later the course of development was steered away from vortex to stratification of the charge. The name stuck anyway and was introduced to the press as such in February 1971, adding to our mental confusion.

The first testbed was an aircooled single-cylinder 300-cc engine with a CVCC stratified-charge head. After this a Honda 600 was modified to the CVCC specifications and used for on-the-road evaluation of the system. Several other engine modifications followed both on Honda's own and other marques, powerplants, which included a Chevrolet Vega unit. The press saw a 2-liter CVCC dual-combustion-chamber engine in a Civic 2-door shell in late 1972; see the February 1973 R&T. A pilot production program was undertaken at the Suzuka Works and several CVCC-powered Civics were produced by normal, though undoubtedly better trained, assembly workers to test mechanical and emission-level tolerance. A fleet of 2-liter CVCC Civics began circulating Honda's famous Suzuka racing circuit day in and day out, much to the chagrin of club racers suddenly robbed of their precious practice time, to accumulate mileage. During 1973 examples of new and "used" CVCC Civics were sent to the U.S. Environmental Protection Agency for emission tests for the 1975 standards, which they passed with no trouble. The American National Academy of Science also awarded its endorsement for the low emission characteristics and practicality of the CVCC system. Earlier a senior Honda director had indicated his preference for a modern, long-stroke engine with uncluttered valve gear layout for CVCC application, but a group of R&D engineers answered this challenge and that of a big engine in a big car by modifying a Chevrolet 350 (5.7-liter) push rod V-8 and submitted the whole Impala thus powered to the EPA. It achieved the stringent original 1975 emission limits, probably to the consternation of the U.S. car industry.

In the meantime Honda formulated the first production CVCC-powered car around the successful Civic theme. The planners reasoned, however, that it would have to have better utility and comfort, and chose a 4-door configuration. The 2-liter prototype engine shrank in size, first to 1.7 and then to 1.6. Finally they decided on a 1488-cc design, which by then was producing enough power and torque to satisfy the needs. The R&D expenditure for the CVCC project was reported to be about $30 million and at its peak more than 600 engineers were mobilized-more than half the R&D engineering staff. And there were many more from production engineering in on the work. To date, four major manufacturers have taken development and production rights to the CVCC principle-Toyota, Isuzu (affiliated with GM), Ford and Chrysler-all adding considerable fortune to Honda's coffer. Said to be under negotiation are pacts with GM and Fiat.


Power Unit

The basic design is an inline 4-cyl engine mounted transversely at the front of the car and inclined 15 degrees forward. The cylinder block is of cast iron-unusual for Honda, long protagonists for light alloy blocks. This material was chosen for its better noise-suppressing ability and production ease, and perhaps room for further capacity enlargement. A single-piece forged crankshaft is supported by five main bearings. In fact, the lower half of the engine is common with the sister 1500 (non-CVCC) unit available in the same body shell. The CVCC cylinder head, of aluminum, has dual combustion chambers. A tiny auxiliary chamber is atop the main combustion chamber the latter having what Honda calls a modified wedge shape with a smoothly contoured wall and no squish area-a testimony that Honda no longer believes in violent turbulence of the charge.

A single belt-driven overhead camshaft operates three valves per cylinder, one intake in the auxiliary chamber and one each intake and exhaust in the main chamber, through rocker arms. The main chamber valves are inline, located across the flame passage from the auxiliary chamber and inclined at 16 deg from the vertical axis of the cylinder. Valve diameters in the main chamber are 34 mm (1.34 in.) for the intake and 30 mm (1.18 in.) for the exhaust, with lifts of 8.7 mm and 8.0 mm respectively. The combustion chamber shape and main valvetrain appear to be shared with the non-CVCC 1500 unit, which probably indicates that they are produced on the same transfer machine - an important cost-saving technique. The auxiliary chamber is made of heat-resistant stainless steel with nickel content, the only unusual material in the whole engine, cast by the lost-wax method and partially machined. The chamber is "dropped" into place, and the auxiliary valve holder is screwed in on top of it. Two gas seals are inserted at the top end of the auxiliary chamber and the valve holder has a rubber oil seal. The auxiliary valve is 12 mm (just 0.47 in.) in diameter and has a 3-mm lift. Small by any other standards, but you may recall Honda once fitted four valves in a cylinder of a 50 cc 3-cyl racing engine that soared up to 23,000 rpm! No dimensions of this "hemi-bottom" auxiliary chamber or its cubic capacity have been released, but I would guess a diameter of about 20 mm ( 3/4 in.) and a capacity of approximately 6 cc. A normal NGK 5ES sparkplug is fitted on the outer side of the chamber at a downward angle: the flame or "torch" passage into the main combustion chamber is at the opposite side, again running at a downward angle almost inline with the plug into the main chamber. The flame passage appears to be larger in diameter and shorter in length than in previous prototype cylinder heads shown to the public: it is about 10-12 mm wide. The auxiliary and main chamber volume ratio, flame-passage size and angle are listed as important and critical factors governing desired stratification of the charge and flame propagation. Valve clearances can be adjusted by normal screw-and-nut methods on the rocker arms. Valve timing is:


  CVCC 1500 Normal 1500
Auxiliary Intake:    
  • Opens, deg ATDC
30 -
  • Closes, deg BBDC
10 -
Main Intake:    
  • Opens, deg ATDC
15 10
  • Closes, deg ABDC
30 30
  • Opens, deg BBDC
30 30
  • Closes, BTDC
15 10


Carburetion is by a Honda-Keihin triple-throat compound downdraft carburetor. It may be more appropriate to describe it as two carburetors in one. A smaller throat, about 7 mm in diameter, has its own float chamber and supplies the rich mixture to the auxiliary chamber. The main chamber's super-lean mixture is handled by the 2 throat progressive-opening unit, the secondary barrel of which opens on manifold vacuum on higher load and rpm. How rich is the rich mixture and how lean the lean mixture? No specific figures here, but my guess is about 8:1 for the former, 20:1 for the latter. The rich just escapes from a plug-fouling condition, but Honda has made sure of positive firing by specifying the wide-range 5ES plug in case the driver should pump the throttle pedal on a cold start. The lean one is definitely outside the firing zone of a conventional engine: only good stratification and flame ignition would burn it effectively. A part of the dense mixture in the auxiliary chamber does run into the main chamber and, diluted with superlean mixture, forms what Honda calls a "mixture cloud" or layers of mixtures with progressively varying densities. A very effective stratification of the charge is thus attained, through which the flame front propogates with certainty and at a controlled rate. Combustion temperature is relatively low, so that formation of NOx is held at a minimum. On the other hand, the combustion process lasts longer than in the conventional engine, allowing an ample hydrocarbon reaction time. Carbon-monoxide emission is inherently low, thanks to the superlean mixture formation. Infrared photography was used in development; temperatures were "read" (by colors of flame through a small window in the combustion chamber.

There is more to the carburetion than providing multiple throats. The aluminum intake manifold is heated by the cast iron dual-chamber exhaust manifold onto which the former is bolted via a heat localizer-shield. This preheating arrangement helps atomization of the incoming charge, just as preheat arrangements do on many current engines. In order to prevent sudden closure of the throttle on deceleration, which caused starvation and breaks combustion rhythm thereby increasing emissions, an elaborate deceleration control system is incorporated. It consists of a dashpot, which damps short-duration lift-offs such as encountered in gear changes, and a solenoid-controlled, speed-sensing and vacuum-operated throttle opener which delays closing of the throttle at speeds over 10 km/h (6 mph). The manually operated choke system has a warning lamp on the instrument panel which lights up if the choke is still pulled when coolant temperature reaches 35 C (95 F). In fact, the choke may better be described as a semiautomatic, as it is partially opened automatically as soon as the engine fires up.

One may be tempted to ask, why not fuel injection? Other know recent developments of the stratified-charge principle, like Ford's Provo, the Texaco system and the Volkswagen prototype, invariably resort to this method of regulating fuel. Honda maintains that the art of its carburetion engineering has become so sophisticated that it affords better control of the charge in their CVCC. And don't think the Honda people haven't tried fuel injection: Honda developed its own injection system for Formula 1 and 2 cars and currently sells a 145 coupe with a radial-pump mechanical injection system. Engineer Kawamoto, one of Honda's young prodigies, concedes that electronics may do the work but adds wryly that an electronic fuel injection not all electronic; imagine a microscopic injection nozzle that shoots and controls fuel into a 6 cc chamber! It would be almost like fuel-injecting a model airplane engine.

As mentioned before, the exhaust manifold is of dual-chamber construction and it has a larger inner capacity. Apparently exhaust gas stays in the chambers longer than in the manifold of the normal 1500 cc engine, and reaction or burning may continue there. No air injection is required, as oxygen content is still high (remember the superlean mixture). There is also a baffling effect in the manifold to direct exhaust gas to the zone that heats the intake manifold. Underhood temperature is slightly higher than in the conventional-engine Civic 1500. After the manifold, the exhaust system is the same as that of the 1500, with a single exhaust pipe and a large-capacity silencer mounted well aft of the system.

Ignition is by a conventional mechanical distributor, but its timing control is elaborate. It incorporates a system for sensing speed, intake-manifold pressure and water temperature to determine advance-retard, in addition to the usual mechanical governor. Standard CVCC ignition timing is 3 BTDC at 900 rpm. The distributor is camshaft driven, and the alternator is driven with the coolant pump by a common belt from the crankshaft. The starting motor is more powerful - output of 1kW - than the unit fitted to the normal 1500 engine, which is a 0.8kW motor. Cooling is by liquid, with a forward-facing radiator, overflow tank and a thermostatically controlled electric fan that comes into action at coolant temperature of 194 F. Lubrication is by wet sump with a rotary pump feeding pressure to vital parts of the engine. The gearbox has a separate splash lubrication system.

The CVCC engine is only slighter larger that the conventional 1500 unit:



Civic 1200

Civic 1500

CVCC 1500

Length, in.












Weight*, lb.




*excluding clutch and radiator but including weight of coolant and lubricant


The CVCC 1500 produces a maximum power of 59 bhp at 5500 rpm and a maximum torque of 69 lb-ft at 3000 rpm on a modest 7.7:1 compression ratio (inclusive of the auxiliary chamber). By comparison, the normal 1500 puts out 60 bhp at 5500 rpm and 70 lb-ft at 3000 rpm on 8.1:1, the high-performance GL version 68 bhp at 5500 and 70 lb-ft at 3500 on 8.6:1, and the current U.S. 1200 52 bhp at 5000 and 59 lb-ft at 3500 on 8.0:1.




Mechanical 4-speed gearbox and Honda's own semiautomatic 2-speed transmission are offered on both the CVCC and the 1500, with different internal ratios. Gearing is one of the critical factors for meeting Japan's 1975 emission standards, which call for a severe low-speed test. The present test mode requires the car to be in the highest gear when it reaches a test maximum speed of 40 kph (25 mph), an absurdly low speed for all practical purposes even in Japan's chaotic traffic conditions. Apparently the CVCC has an effective low-emission speed range, and in order to keep the engine operating in this "reaction" range the car must suffer low gearing, at least in the home versions. Internal ratios of the CVCC and the normal 1500 are:









































Honda has added a hydraulic clutch damper to the single-dry-plate diaphragm clutch to give a slight delay, 0.15 to 0.19 seconds, when the clutch is let in. This improves the "feel" and ensures longevity, say the engineers.

In Japan, Honda's 2-speed semiautomatic transmission is promoted as a "stepless automatic", relying solely on its high stall-ratio torque converter with 1st gear in the 2-speed constant-mesh gearbox considered as an emergency low. The converter is of Honda design and manufacture and has a stall ratio of 2.75:1 (vs around 2.0:1 for most converters) and stall speed between 2600 and 2800 rpm, which must certainly be an optimum compromise of efficiency and performance. This simple semiautomatic works remarkably well in the light Civic shell. Honda did not touch the 1st-gear ratio for the CVCC; the car was apparently driven off in 2nd gear in the official emission test. Only the "D" range ratio was raised numerically.


The Car

The Civic 4-door sedan is longer by 5.9 in. than the 2- or 3-door version and its wheelbase is extended by 3.2 in. Width, height and tracks are unchanged. The CVCC GF sedan, the top of the range, scales 1645 lb in Japanese version with manual gearbox, of which 1050 lb is on the front wheels. Suspension is basically unchanged: all-independent by MacPherson struts. The front suspension is further located by diagonal links and angled transverse arms; roll is checked by a conventional anti-roll bar. At the rear end the strut is located by a pressed angled-forward transverse arm and an angled-rearward rod, a system affectionately called "Sakata suspension" after an enthusiastic chassis designer who successfully resisted a suggested reversion to a dead beam axle on a pair of semi-ellitpics. His argument was that a well-located dead axle system would weigh more than his light independent one. Sakata was, however, well aware of the criticism against the harsh ride of the Civic and has given the 4-door more generous amounts of rubber at strategic suspension pivots. Steering is straight from the smaller Civic, a pleasant rack and pinion system calling for 3.1 turns of the wheel from lock-to-lock. The column now incorporates a collapsible section. The steering wheel diameter is 4 inches larger and it is slightly more dished, bringing the wheel close to the driver. Brakes are front Girling 8.9 inch discs and rear 7.1 inch drums, vacuum assisted with diagonally interconnected dual hydraulic circuits. Tires and wheels are also carried over from the 2- and 3-door models: cross-ply 6.00S-12 on 4J pressed steel wheels. Optionally available is a Honda-designed, Hitachi-built air-conditioning system.


Driving the CVCC Civic

Honda arrayed 42 4-door Civics for press appraisal - an ominous number like your 13, but these are the last people to be swayed by superstition. Of this large fleet of new cars, nearly two-thirds were powered by CVCC engines. The nose of the 4-door sedan has been extended to accommodate the larger power unit and the rake of the rear window is increased giving a more balanced look. Luggage volume benefits from the stretched length but is still rather small. The rear-seat leg room is on a par with the average 1.4/1.6 litre Japanese car and together with wind-down windows, helps relieve the occupants of the closed-in feel of the smaller Civic.

Drivability of the CVCC Civic is excellent. The only peculiarities I noted were slightly different noise from the engine, by no means obtrusive, and less braking effect on lift-offs - the latter symptom to be expected of the deceleration control system in the carburetor. In fact, several other cars of non-Honda marque meeting 1973 emission standards use similar deceleration control mechanisms. Faced with a novel power unit, one would try hard to find its faults by subjecting it to a series of cruel tests: Slog on in top gear at mere 1200 rpm. Climb down a gentle hill at high speeds and light engine load, and at the bottom, slam on the loud pedal. Reserve a car, leave it in the cold while enjoying a leisurely lunch, after which drive off without warming up. The CVCC did not protest, and functioned its given shores willingly and obediently. The only complaint I had was the low gearing. The Civic engines, both CVCC and normal 1500, have an exhaust resonance period beginning at about 4000 rpm. It is louder in the CVCC, probably because of its larger-capacity exhaust manifold, and because of the lower gearing it coincides with Japan's top legal speed of 100 km/h (62 (mph). On some CVCC models it was slightly higher, 105 to 110 km/h. It was the designer's intention to "chase away" this resonance period to above 120 km/h, but apparently he could not achieve it.

Thanks to the longer wheelbase and generally refined suspension, the 4-door Civic rides quite decently, comparable to European small cars, but the steering feels a bit heavy because of the car's increased front weight bias. That nice tautness of the smaller Civic has been somehow lost, but the general feel is in character for a 4-door family sedan.

No fuel-consumption figures were taken during the short test period, but President Kawashima proclaimed that had the CVCC Civic been inferior in fuel economy to the average Japanese 1.4/1.6 litre car, his company would not have released the car at this most difficult time - amid the current fuel shortage. Then Director Sugiura, head of R & D, quoted the following figures obtained in their own test programs.



Avg 25-mph city


Avg 36-mph highway


Three Japanese cars (non-Honda 1400 to 1600)



Normal Civic 1500



CVCC 1500

Japanese Specs



CVCC 1500

U.S. specs




Here the low gearing of the homemarket CVCC puts a penalty on fuel economy, and for once the U.S. version has an advantage. Still, the CVCC performance is quite impressive.


Honda Civic CVCC Emissions Performance


    Emissions, gram/mile  




1975 Federal limits,

before EPA revisions




1975 Federal limits,

now effective




1975 California limits,

now effective




Honda Civic CVCC




After 50,000 miles





WHAT PRICE clean air? An extra expenditure of about $100, taking all the current tax-reduction bonus, over the price of the normal 1500 65-hp Civic 4-door sedan. The premium will thus be higher in the U.S. But you might enjoy the puzzled countenance of a police officer whose CO counter won't even flicker its needle.





The Saitama factory is geared to produce 10,000 4-doors a month.


APRIL 1974