Quote:
Originally Posted by martae
Great job Basjoos, but why didn't you start with a civic VX instead of a CX ? It was the high mileage model. Feather light aluminum wheels. Wider ratio transmission with a higher final drive ratio (2000 rpm at 60 mph). Variable valve timing with a twist. In this engine only one intake valve opens below 2500 rpm. Since there is only one intake valve open more of the pressure drop between the atmosphere and the cylinder is across the valve rather than the throttle plate. This gives a more turbulent fuel air mixture which allows a leaner fuel/air charge, greater torque at low engine speed, and no predetonation . The use of a very sensitive oxygen sensor (unique to the VX) allows more precise control of the FA mixture making a very low idle possible. On a warm day mine idles at about 500 rpm. The practical effect of these engine tweaks is high torque at low RPM sort of like a diesel. As I'm sure you guys know, the great weakness of the Otto cycle (the spark igniton gasoline engine is an Otto cycle engine) are the large pumping losses at part load caused by sucking the FA charge past the throttle plate. The ability of this engine to deliver good torque at low RPM (and thus lower pumping losses) is the secret to the high fuel economy this car delivers. The CX and the VX share the same body, but the CX is listed at EPA 42/46 and the VX at 47/56. The VX also offers higher power since the engine has the same displacement, but four valves per cylinder (92 vs 70). I bought mine new in 1992, have put 208 thousand miles on it and still average 45 mpg to work and around town. When the car was new 52 or 53 mpg was not unusual on a long road trip. The fact Honda could do this with the technology of 15 years ago shows what a bunch of liars the auto companies are when they squeal about a 35 mpg average fuel economy rule.
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I started with a CX (which I had bought new in 92) rather than a VX because that was the car I was driving at the time I decided to start aero modding my car. The CX and VX share the same transmission. The main differences being the in engine,, lighter wheels, some additional interior features in the VX (the CX is the bare bones Civic model) and some underbody aero to slightly reduce the Cd of the VX. The VX and CX have the same weight. When new, my CX typically gave me 51mpg on the highway in the summer (44mpg highway in the winter) and 38mpg was the worst I ever got with it (in snow driving and winter tires). Interestingly, when I installed a DX engine at 245,000 miles (but kept the same transmission), the mileage remained the same, but my 0 to 60 times dropped to 10 sec.