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	Merits of Direct-Actuated Type Variable Valve Control System, HYPER VTEC Direct-actuated type variable valve control system, HYPER VTEC, developed with the aim of reconciling high revolution and high power performance for sports type motorcycle engines and environmental performance. Ease of handling over the whole ranges from low to medium speed revolution to high-speed revolution and the feeling of sporty acceleration, improvement of fuel consumption rate and even the reduction of driving noise mainly of intake and exhaust sound, not to mention the improvement of power have been realized. Through the development of the HYPER VTEC, Honda realized simple and compact variable valve control system, which enabled high-speed revolution of over 10,000rpm and further evolved VTEC.

Engine Output Characteristic

Comparison of power characteristic of HYPER VTEC engines and the base engines having the conventional valve mechanism shows that power improvement is seen in medium and low speed range in the engines adopting HYPER VTEC and improvement is attempted also in high-speed range by designing intake and exhaust system suited for high-speed range. Power improvement in medium and low speed range enabled to materialized power characteristic easy to handle and sharp feeling of acceleration is obtained by the change in torque characteristic at switchover from two to four valves.

Reduction of Friction and Improvement of Fuel Consumption Rate

According to the results of friction measurement of kinetic valve system of HYPER VTEC engines, friction increases also in the range where four valves are put into operation. In the range where two valves are operated, the friction is reduced as compared with the base engines equipped with conventional valve mechanism, and thus contribute to the improvement of fuel consumption rate by approximately 5.5% in EC40 mode.

Reduction of Friction and Improvement of Fuel Consumption Rate

Effect of Reducing Drive Noise

HYPER VTEC has an effect of reducing the sound of intake and exhaust system in the range where two valves are working. According to an analysis of the driving noise frequency, a reduction of 2 to 5dB was seen as compared with base engines in each frequency zone mainly in the areas of intake and exhaust sound below 1kHz. Accelerated drive noise measured by the method specified by European legal control (EEC87/56) was reduced by 1.7 ~ 2.0dB both in the second gear and third gear despite an increase in the speed from approximately 10 to 15%.
Concerning the mechanism of drive noise reduction, it was confirmed that the sound pressure level inside the induction and exhaust pipes was reduced with the shift to two valves, and at certain revolution range the blow-down pressure was reduced at the beginning of the opening of the exhaust valves and the spitting from the exhaust system to intake system decreased at the time of valve overlap. Those are considered attributable to the reduction of intake and exhaust sounds.

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