Motivation is the key to every project vehicle, and Rob Walker's inspiration came in the form of a collision with a deer on a dark and deserted highway. For Walker, it proved to be the ideal time to revamp his 1990 Civic Si into something more than just a daily driver. While his car sustained major damage from the accident, Walker knew he could massage it back to health with the right engine, suspension and body treatments that would breathe some new life into this decade old platform.
Walker's game plan called for a power bump that had to be 100 percent bulletproof, so a B16A engine, transmission and ECU was ordered from a tuner shop in Japan. Compared with the stock D16A6 motor, the Japanese-spec unit enjoys a negligible 5cc gain in displacement. Yet, the 1595cc's of combustible volume are put to work much more efficiently due to a vastly better cylinder head, more aggressive cams and the increase in compression ratio from 9.2:1 to 10.2:1.
How exactly does increasing an engine's compression ratio improve power? As we all know by now, the engine in your car converts chemical energy to mechanical energy. The measure of how well this conversion takes place is termed thermal efficiency (TE). Typically, less than a third of the available chemical energy ever acts on driving the piston. The rest is wasted in the form of heat. Some factors that determine the TE of an engine include piston and combustion chamber design, alloy content, special coatings, ignition timing and compression ratio (CR). If you can increase the TE through one or more of these factors, more power will result.
CR is calculated by the ratio of the chamber volume, while the piston is at BDC (bottom dead center) vs. TDC (top dead center). This is the mechanical (static) CR, which is what's commonly referred to in manufacturer's specs.
Keep in mind that in a running engine; the actual CR can be altered by the cam profile.
For instance, if the cams keep one or both (overlap) of the valves slightly open during part of the compression stroke, the CR will actually be lower, because some of the mixture will have escaped out of the chamber. The resultant CR is known as the effective (dynamic) CR.
In higher CR engines, more air and fuel molecules become packed into a smaller area during the compression stroke. This increase in mixture density will result in a bigger explosion, which means that more of the heat of the combustion will get transferred into the air within the cylinder to drive the piston instead of the walls of the combustion chamber for your cooling system to deal with.
Unfortunately, no engine is 100 percent thermally efficient. In fact, internal combustion engines are terribly inefficient. Once you factor driveline and thermal losses into the equation, it gets down right depressing. The primary byproduct of this hotter burn is an increase in temperature, resulting in the likelihood of detonation, or knock. As long as the engine is properly tuned, you will be able to enjoy the extra power any which way you want.
To make sure that every bit of power gets unleashed, an AEM cold air intake, DC header and custom 2.25-inch, stainless-steel exhaust system help usher the air through the powerplant. Four degrees of advance and 1 degree of retard were dialed-in with AEM camshaft gears were used to manipulate the torque band to Walker's liking. A 2G Integra shifter linkage was cut and welded to stir the transmission gears. The entire set-up bolts to the chassis via homegrown motor mounts. Walker and his friend, Bud Khuns of Zoom Motorsports, did all of the work in their spare time.
By Stephen H. Chu
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