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REV born from aiming at reconciliation of 200PS per liter and
low revolution range performance |
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Honda CBR400F equipped with REV, marketed in 1983
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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.
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Starting point of VTEC.
Revolution responding type valve pausing mechanism "REV" |
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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.
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VTEC meeting with various requirements, such as practical use
types and low fuel consumption types |
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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.
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Intelligent new-generation engines, DOHC i-VTEC |
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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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