Porsche 911 Turbo User Handbook Manual page 20

VarioCam Plus.
Optimum valve timing, optimum valve lift, in all load conditions.
VarioCam Plus is a variable valve Essentially, VarioCam Plus makes
timing system on the inlet side two engines out of one. The first is
which also features two-stage valve geared for normal road driving,
lift. The benefits it provides the second for high-performance
include greater power and torque use. The system switches seam-
at all engine speeds, as well lessly between the two as
as smoother running, better fuel driver inputs change. All operations
economy and fewer emissions. are controlled by the engine
management system. The result:
emphatic acceleration and smoother
running.
The two-stage lift mechanism
on each inlet valve consists of an
electro-hydraulically switchable
tappet. Each of the 12 tappets
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consists of two concentric parts – The timing of each valve is
an outer ring and a central shaft – steplessly controlled by means of
which can be locked together an electro-hydraulic rotary vane
by means of a pin. The system adjuster at the head of the cor-
can then vary the valve lift by responding camshaft.
using two large profile cams on
the outer ring or a smaller cam To improve responsiveness
lobe on the central shaft. during warm-up in cold weather,
VarioCam Plus will select the
higher valve lift setting and retard
valve timing.
911 Turbo |
At medium revs and low engine
loads, the lower valve lift setting
is selected and timing advanced in
order to reduce fuel consumption
and emissions. The economy of
the engine is particularly enhanced
at lower engine speeds. For
maximum power and torque, the
higher lift setting is selected
and the timing of the valves is
advanced.
From the driver's perspective,
the benefits are obvious: copious
torque and exceptional fuel
economy, particularly in comparison
with much larger engines offering
similar power output.
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Drive