About the Honda Civic VX

During the late 1980s and the early 1990s, as a result of high gasoline prices and the consumer demand for relief, automobile companies, particularly Toyota and Honda competed to see who could field the most fuel efficient production automobile. The Civic VX was Honda's entry for 1992.

Fitted with the same manual transmission as the USDM CX, the VX was identical to the base model CX except that it gained improved fuel efficiency from various weight reduction methods such as reduced trim and molding, VX model-specific lightweight 13" aluminum alloy wheels, 165/70/R13 tires, and through a 92 hp (69 kW) 1.5 L (D15Z1) VTEC-E engine. These features on the VX yielded 48/55 mpg (city/hwy) [revised to 2008 EPA rating: 39/49 mpg city/hwy[5]] or 44/51 mpg (city/hwy) [revised to 2008 EPA rating: 36/46 mpg city/hwy[6]]

The D15Z1 engine's efficiency was enhanced by placing cam followers(bearings) at every cam lobe, to reduce friction, the use of only two piston rings per cylinder, to reduce friction, and the ability to burn an ultra lean(for the time) fuel air mixture at idle, and below 2500 rpm at low load. This was achieved by only opening one valve during the intake stroke, rather than both, below 2500 rpm engine speed, placing the multiport fuel injectors very near the intake valves, and by using an ultra sensitive oxygen (lambda) sensor. The oxygen sensor is mounted on the cast iron exhaust manifold, to be as close to the cylinders as possible, so the sensor will be as hot as possible for more accurate readings. It has two O2 measurement electrochemical cells, rather than the single cell that at the time was universal. This same model sensor has been adopted by racing teams to monitor the combustion in each cylinder of racing engines during the tuning process, one per cylinder, because of its sensitivity.

The opening of only one intake valve below 2,500 RPM results in much more of the pressure drop between atmospheric pressure, and the inside of the cylinder to be across the valve than would otherwise be the case. This results in an exceptionally turbulent flow, very good mixing of the charge, very high speed flame propagation at ignition, high resistance to predetonation (knock), and very low amounts of unburned hydrocarbons, and carbon monoxide, and increased engine torque, and power in both lean burn mode, and at more normal fuel-air mixtures, below 2,500 rpm. As a result of, the increased torque, and power at low rpm, the engine's torque, and power curves are between those of normally aspirated gasoline, and diesel engines. Since the VX has what was for the time an ultra low coefficient of aerodynamic drag of 0.30 cd, the car could operate at highway speeds in lean burn mode.

The D15Z1 engine was considered revolutionary for its day. To this day, the VX remains a favorite of Hypermilers.

One of the few rocks Honda left unturned in search of better fuel economy was increasing the final drive ratio of the VX, usually expressed as the number of engine revolutions per mile in the transmission's top gear. Since the ratio of the VX is identical to the CX, despite the engine's greater power, low end torque, and the car's lower coefficient of drag the use of a higher final drive ratio would have resulted in a drivable car, with even higher fuel economy. The lower than necessary final drive ratio results in a vehicle that is remarkably quick off the line, for one that can get 50 MPG on the highway. A higher ratio could have been accomplished by transmission modifications, such as an overdrive top gear, a dual range transmission, or simply by using larger diameter wheels, in conjunction with a wide ratio transmission, so there would be sufficient torque on the driving wheels in first gear.

In Canada, the VX was rated by Transport Canada fuel consumption estimate: 4.7L/100 km city and 4.3L/100 km hwy.[7] Other added features were an 8000 rpm tachometer with redline at 6000 rpm, lightweight 13-inch (330 mm) aluminum alloy wheels, as well as additional front & rear under-body trim additions to improve aerodynamic flow. The VX was also equipped with an aluminum alternator bracket, an aluminum front driver's side engine mount, and a lightweight crank pulley. In addition, the instrument cluster of the CX and VX featured a shift indicator light that would notify the driver when to shift upward in order to achieve optimum fuel economy. To this day, the CX & VX models are lauded as one of the only gasoline-powered cars that rival the fuel economy of today's hybrids and diesels. In the March 2010 issue of Car & Driver for example, it mentions its long-term test car, a 2009 VW TDI Jetta with 6-speed dual-clutch auto transmission, got worse fuel mileage (38 mpg) than their 1992 Honda Civic VX test car (which got 41 mpg) and 2000 Honda Insight hybrid (48 mpg).[8]

-Wikipedia