Honda Acura NSX 1991 Service Manual page 50

Variable Valve Timing and Lift Electronic
Control System (VTEC)
Mechanism
At Low rpm:
As shown, the primary and secondary rocker arms located on both sides are not connected to the mid rocker arm but are
driven separately by cam lobes A and B at different timing and lift. Although the mid rocker arm is following the center
cam lobe with the lost-motion assembly, it has no effect on the opening and closing of the valves in the low rpm range.
rpm:
At Low
HYDRAU
PISTON (B) /
At High rpm:
When driving at high rpm, the built-in piston moves in the direction shown by the arrow in the figure below. As a result,
the primary, secondary, and mid rocker arms are linked by 2 hydraulic pistons (like a skewer) and the 3 rocker arms move
as a single unit. In this state, all the rocker arms are driven by cam lobe C opening and closing the valves at the valve tim-
ing and lift set for high operation.
At High rpm:
5-6
I
PRIMARY MID
ROCKER ARM ROCKER ARM
I
PISTON (B)
CAM PROFILES FOR
"A
drive the rocker arms
separately.
R E T U R N S P R I N G
STOPPER PISTON
\
SECONDARY
R O C K E R A R M
CAM PROFILES FOR
HIGH RPM
'The rocker arms are linked
via the hydraulic piston.
Cam lobe C drives the rocker
arms.
STOPPER
PISTON
and 6 cam lobes