From REV to VTEC. Variable Valve Control System ever evolving

It can be said that VTEC, the original Honda variable valve control system originated from REV, revolution responding type valve pausing mechanism, announced in 1983. Receiving the demand for high power for sports bike engines at that time, prior study was started to reconcile high power in high revolution range and excellent drivability and high efficiency from idling throughout all ranges. An epoch-making variable valve system came into being, which enables to switch over from two valves to four valves. This technology later developed into the variable valve timing mechanism, VTEC (variable valve timing and lift electronic control system), which forms the nucleus of automobile engines.

REV born from aiming at reconciliation of 200PS per liter and low revolution range performance
CBR400F
Honda CBR400F equipped with REV, marketed in 1983
Faced with the demand for high power for sports bike engines, a preceding study started off on the assumption of 200PS performance per liter and the development of mass production engines with drivability from the same idling as before. The assignments for the project were to achieve the target power performance and come up with countermeasures against power drop in low speed revolution range and improper idling. It was revealed in the analysis of these issues that the large bore ports for achieving high revolution and high power and for reducing air inlet resistance and the intake and exhaust system with a pleural number of intake and exhaust valves hindered obtaining good idling and low and medium speed revolutions.
An experiment conducted by forcibly stopping several multiple valves made it possible to confirm the stability of idling and a dramatic improvement in the power of low and medium speed revolution range. This was the starting point for the development of valve pausing mechanism (REV: Revolution-modulated valve control), which was applied to the CBR400F in 1983.

Starting point of VTEC.
Revolution responding type valve pausing mechanism "REV"
REV is a system to operate four valves in high speed revolution range in accordance with the revolution of engines and to reduce the number to two valves in low and medium speed revolution range. Pause the operation of valves on both inlet and exhaust sides at the rate of one each per cylinder. A sensor detects the revolution of engines. Four valve operation and two valve operation are automatically changed over, performing the separation and connection of locker-arms by the shift of hydraulic pistons built inside the locker-arms split into two. When four valves are in operation, high power is produced in high speed revolution range while two valves are put into operation, blow-by of fuel air mixture is reduced, so that flow velocity is improved. A high swirl effect and excellent filling efficiency will materialize power improvement in low and medium speed revolution range.
VTEC meeting with various requirements, such as practical use types and low fuel consumption types
VTEC engines started from the REV for motorcycles have undergone subsequently various evolutions. DOHC VTEC engines with switchover for valve timing and the amount of lift for intake and exhaust system aiming at high power and high torque. VTEC engines with a single cam shaft to drive intake valves, switching over low speed valve timing lift and high speed valve timing lift by attaching importance to the balance in the practical use range. Furthermore, VTEC-E engines, which attempted substantial improvement of fuel consumption by enabling lean burn, suspending one valve in low speed range, in addition to the driving by practical valve timing lift in medium and high-speed range. And, 3 STAGE VTEC engines were put out. Switchover was made literally into three stages, using three cams for low, medium and high-speed operations on air inlet side, suspending one valve at low speed operation and taking switchover motion to valve timing lift in medium speed and high-speed operations.
Intelligent new-generation engines, DOHC i-VTEC
Honda has further evolved VTEC and newly developed DOHC i-VTEC, reconciling low fuel consumption of world top class and clean exhaust gas and having high power and rich torque characteristics over the entire ranges. For this engine, highly intelligent valve timing lift mechanism, which combines Honda's original VTEC switching over valve timing and the amount of lift in accordance with the revolution ranges of engines with VTC (variable timing control) continually controlling the phase of air inlet valve timing in accordance with the load on engines.


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