Direct-actuated type HYPER VTEC Reconciling High Revolution and High Power and Environmental Performance

In sports type motorcycle engines, especially in 4-stroke engines of medium displacement, the maximum revolution reaches to a level as high as 13,500rpm. To cope with such high revolution, Asaka R&D Center has developed a compact and simple "direct-actuated" type variable valve control system, HYPER VTEC. This is an epoch-making system as switchover is made from two-valves to 4-valves per cylinder in the low and medium speed range and the high speed range is completed in the valve lifter without using the locker-arms, so the increase of mass is checked of the kinetic valve system and the ease of operation is secured in high revolution range.

Points of HYPER VTEC development
In January 1999, valve control system for 4-stroke engines, HYPER VTEC, was announced.
It was put on sale, mounting on the new sports bike, CB400 SUPER FOUR.
HYPER VTEC is a valve pausing system, further advancing VTEC technology through hydraulic control unique of Honda, in pursuit of the improvement in the suction, exhaust efficiency and combustion efficiency of 4-cycle engines. A direct-actuated type is adopted, in which cams will directly push up the valves through lifters. The system enabled to switch over the number of valve operations per cylinder between low and medium speed revolution range and high speed revolution range, and by setting cam profiles to give optimum valve timing to the valves on working side and on paused side, power output characteristics were demonstrated in the low and medium speed revolution range and in the high speed revolution range for further improvement in fuel consumption rate.
Further Evolution to HYPER VTEC SPEC II and III
HYPER VTEC keeps on evolving, without slackening.
In January 2002, HYPER VTEC evolved into Spec II aiming at letting everybody actually feel the power drive over the entire ranges. As one of the aims of Spec II development, it can be pointed out that the CB400 SUPER FOUR, the model on which the system was installed, is the one having a wide user class. There were voices to point out that beginners, in particular, were unable to fully utilize the four-valve stage from above the revolution range of 6,700. The development team then developed HYPER VTEC SPEC II anew to enable many more users to enjoy the four-valve stage of HYPER VTEC.
SPEC II achieved increasing torque in the middle speed range and smoother power by refining the valve timing, inteke and exhaust systems, and the valve switchover timing revolution from two to four valves was changed from 6,750rpm to 6,300rpm. It has resulted in powerful and sporty engines, enabling one to actually feel VTEC in all driving ranges from low to top. In December 2003, SPEC III was introduced. The switchover timing for a 6 speed only was changed from 6,300rpm to 6,750rpm to improve fuel consumption in cruising over high speed roads without spoiling the cheerful drive.


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