Control System (VTEC)
Outline
The engine is equipped with multiple cam lobes per cylinder, providing one valve timing and lift profile at low speed and a
different profile at high speed. Switch-over from one profile to the other is controlled electronially, and is selected by
monitoring current engine speed and load.
CAM LOBES FOR LOW RPM
CAM LOBES FOR HIGH RPM
PRIMARY ROCKER ARM
MID ROCKER ARM
SECONDARY ROCKER ARM
LOST MOTION ASSEMBLY
INTAKE VALVE
EXHAUST VALVE
In general, it would be ideal if the high rpm performance of a racing engine and the low rpm performance of a standard
passenger car engine could be combined in a single engine. This would result in a maximum performance engine with a
wide power band. Two of the major differences between racing engines and standard engines are the timing of the in-
take/exhaust valves and the degree of valve lift. Racing engines have longer intake/exhaust timing and a higher valve lift
than standard engines. The Honda Variable Valve Timing and Valve Lift Electronic Control System takes this into ac-
count. When valve actuation is set for low rpm timing and lift, low rpm torque is better than in a standard engine. When
valve actuation is then switched for high rpm timing and lift, output improves to the level given by a racing engine. Until
now, few variable valve timing systems have been commercialized. In those that have, only the time that both valves are
open (intake/exhaust overlap) could be changed. Honda’s system is the first in the world in which both the valve timing
and the degree of valve lift can be changed as needed, making it the most advanced valve train mechanism available.
Valve Timing
(exhaust/intake)
Valve Lift
Racing Engine
Exhaust Intake
VTEC Engine
Low High Low
Exhaust Intake
Standard Engine
Exhaust Intake
Max. Power
Low rpm Torque
Idling Stability
TDC = Top Dead Center
Low rpm High rpm
VTEC engine
RPM switch over
point
Standard engine
rpm
BDC = Bottom Dead Center
O = Optimum Characteristic
The engine is equipped with two valve timing and valve lift settings which change according to driving conditions.