Honda Civic Service Manual page 237

Fuel and Emissions Systems
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System Descriptions (cont'dl
VTC system
. The VTC system makes continuous intake valve timing changes based on operating conditions.
. Intake valve timing is optimized to allow the engine to produce maximum power.
' C a m a n g l e i s a d v a n c e d t o o b t a i n t h e E G R e f f e c t a n d r e d u c e t h e p u m p i n g l o s s . T h e i n t a k e v a l v e i s c l o s e d q u i c k l y t o
reduce the entry of the airlfuel mixture into the intake port and improve the charging effect.
. Cam angle is reduced at idle to stabilize combustion and reduces engine speed.
' l f a m a l f u n c t i o n o c c u r s , t h e V T C s y s t e m c o n t r o l i s d i s a b l e d a n d t h e v a l v e t i m i n g i s f i x e d a t t h e f u l l y r e t a r d e d p o s i t i o n .
MAXIMUM VTC ADVANCE 50'
i
l(-4
sHoRT oVERLAP
'+-|l
LoNG oVERLAP
VTEC system
' The VTEC system changes the cam profile to correspond to engine speed. lt maximizes torque at low engine speed
and output at high engine speed.
. The low lift cam is used at low engine speeds, and the high lift cam is used at high engine speeds.
LOW SPEED VALVE TIMING
HIGH SPEED VALVE TIMING
TDC
MAXIMUM VTC ADVANCE 50'
1 1 - 3 0