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While the 4G63 power plant was retained, it underwent extensive modifications.
In addition to the use of a high-speed cam profile and lighter pistons,
Evolution IV reduced turbo lag by minimizing gas flow interference
in the exhaust manifold. The introduction of a twin-scroll turbocharger
improved supercharging performance, generating more torque in the
low and medium range. Evolution IV also featured a straighter intake
manifold, and a metal head gasket that withstood the higher compression
ratio and boost pressures better. The introduction of a secondary
air induction system improved turbo on-off response by feeding pressurized
air above the turbine and reducing negative pressure, thereby keeping
turbine speed from dropping under deceleration. All this new technology
realized a substantial increase in engine performance, pushing maximum
power output up to 280PS at 6500rpm and maximum torque to 36.0Kg-m
at 3000rpm.
In addition to the standard close-ratio 5-speed manual transmission, Evolution IV was offered with a super-close-ratio gearbox. And a choice of high or low final drive gears made Evolution IV easier to tune for competitive use. The RS model, developed primarily as a base vehicle for competition use, was offered with a torque-adaptive helical gear limitedslip front differential - a world first on a 4WD model. And the rear differential incorporated another world first: Active Yaw Control. Generating a stabilizing yaw moment by creating a torque differential in the rear wheels, AYC realized a significant improvement in cornering performance and in vehicle stability under hard braking. Evolution IV saw a shift towards more on-road testing during development, enabling it to evolve into a machine capable of showing the opposition just as clean pair of heels on the circular track as in rallies. |
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