change wheel PORSCHE 911 GT2 2008 5.G Information Manual

· 20 ·· 21 ·The 911 GT2 |
Drive
At Porsche, our aim is not to
increase power – except through
increased efficiency. Which is
why we began with the 911 Turbo
when developing an engine for
the 911 GT2. Its power is com-
bined with rear-wheel drive for
racing-car driving dynamics. But
how is it possible to improve onan engine that is already so close
to perfection? How did we introduce
even greater potential – and the
character of a racing engine? The
answer: by increasing efficiency.
This was mainly achieved by four
crucial components, one of these
being the six-cylinder twin-turboboxer unit with flow-optimised
turbines featuring Variable Turbine
Geometry (VTG, see page 28)
and larger compressors on the
intake side. Together with
VarioCam Plus (see page 26), they
boost performance while reducing
emissions over the entire engine
speed range. Also with the innovative expansion intake system
which works on highly efficient
principles that are contrary to all
previous methods (see page 32).
In addition, the new lightweight
rear silencer made from titanium
enhances performance by producing
less back-pressure through the
exhaust system.
Oil is evenly distributed under all
load conditions (e.g., high-speed
cornering) thanks to a dry-sump
lubrication system with external
tank. After passing through the
engine, the oil is cooled by means
of a dedicated oil-water heat
exchanger. Both of these systems
are proven in competition use.
The water-cooled flat-six twin-turbo
engine with four-valve technology
in the rear of the 911 GT2
generates a mighty 390 kW
(530 hp) from a 3.6-litre
displacement at 6,500 rpm.
Maximum torque of 680 Nm is
achieved at low rpm and sustained
across much of the engine
speed range. It is available
between 2,200 and 4,500 rpm
and the resulting acceleration is
quite literally breathtaking.
300 500 550
600
650
700 750 800
850
280 300 320 340 360
380
400
2000 3000 4000 5000 6000 7000
350 400
450
1000
Power (kW)
Engine Speed (rpm)
180 200 220 240 260 420
900
Torque (Nm)
390 kW (530 hp)
680 Nm
The benchmark sprint to 100 km/ h
(62 mph) is completed in
3.7 seconds; 200 km / h (124 mph)
requires just 11.2 seconds.
Maximum speed – if you really
want to put it to the test – is
329 km / h (204 mph). Even more
impressive is the power-to-weight
ratio of 361 hp per tonne and
the specific power output of
147 hp per litre. Fuel economy
is also exceptional for a car
with such high performance.
There is nothing ordinary about
the 911 GT2 and it exceeds even
the highest expectations. In
other words: everything you’d
expect from the most powerful
road-going 911.
911 GT2 : 680 Nm from 2,200 to 4,500 rpm, 390 kW (530 hp) at 6,500 rpm 3.6-litre twin-turbo boxer engine
The greatest strength comes from within.
Engine.

· 26 ·· 27 ·
The 911 GT2 |Drive
VarioCam Plus
Engine cooling.
The engine of the 911 GT2 features
cross-flow water cooling with fully
integrated coolant management.
This technology ensures a consis-
tent flow of coolant to each of
the engine’s cylinders. Waste
heat from the oil is transferred to
the coolant via two oil/water heat
exchangers. The coolant is routed
through twin radiator modules
ahead of the front wheels and a
centrally placed unit in the nose.
VarioCam Plus.
VarioCam Plus is a variable valve
timing system on the inlet side
which also features two-stage valve
lift. The benefits it provides include
greater power and torque at all
engine speeds, as well as excellent
running characteristics, better fuel
economy and fewer emissions.
Essentially, VarioCam Plus makes
two engines out of one. The first is
geared for normal road driving, thesecond for high-performance use.
The system switches seamlessly
between the two as the driver
inputs change. All operations
are controlled by the engine
management system. The results:
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 con-
sists of two concentric parts – anouter ring and a central shaft –
which can be locked together by
means of a pin. The system can
then vary the valve lift by using
two large profile cams on the outer
ring or a smaller cam lobe on the
central shaft. The timing of each
valve is steplessly controlled by
means of an electro-hydraulic
rotary vane adjuster at the head
of the corresponding camshaft.
To improve responsiveness during
warm-up in cold weather, VarioCam
Plus will select the higher valve
lift setting and retard valve timing.
At medium revs and low engine
loads, the lower valve lift setting
is activated and timing advanced in
order to reduce fuel consumption
and emissions. The economy of
the engine is particularly enhanced
at lower engine speeds. For maxi-
mum power and torque, the higher
lift setting is selected and the tim-
ing of the valves is advanced.This results in copious torque
and exceptional fuel economy,
particularly in comparison with
much larger engines offering
similar power output.

· 39 · · 38 ·
The 911 GT2 |Drive
The six-speed manual gearbox in
the 911 GT2 is specifically
designed for the high engine
performance. The individual ratios
are carefully matched to the spe-
cific characteristics of the engine.The gear-lever throw is short and
precise, enabling fast and
accurate gearshifts.
A typical feature of the 911 GT2
is the Launch Assistant – for maximum acceleration from a
standing start. The clutch and
accelerator are depressed when
the vehicle is stationary.
When a
boost pressure of approximately
0.9 bar is displayed in the instru-ment
cluster, release the clutchas
quickly as possible and maximum
a
cceleration automatically ensues.
Normally on a turbocharged vehicle
with manual gearbox, the boost
pressure under acceleration from
a standing start is relatively low.
The turbo effect is delayed as
the engine gathers speed and
the boost pressure starts to build.On the 911 GT2, this initial delay
is reduced. While the car is still
stationary, the fuel injection is
modified to help the engine reach
maximum output earlier. The boost
pressure is significantly increased
and the engine readied for a faster
start.
A specially designed traction
control system adapts the acceler-
ation procedure automatically
in the ECU to ensure optimum
traction. The clutch remains
engaged. This reduces load and
prevents high clutch wear. The
power is transmitted directly to
the road via the rear axle.
The gearbox is combined with
a cable linkage and dual-mass fly-
wheel offering added comfort and
precision. The close ratio spread
enables powerful acceleration
within the optimum engine power
band.
Steel baulk rings on gears two to
five ensure a precise gearshift
action even under extreme loads.Cooling is provided by an add-
itional oil-to-water heat exchanger
and spray lubrication. Both of
these features are essential for
durability in endurance racing
conditions.
Other standard features include
a limited-slip differential with
asymmetrical lock factor. Offering
better traction and handling
when exiting a corner, it applies a
higher proportion of drive torque
to the loaded outer rear wheel.
The term ‘asymmetrical’ means
that one lock factor is applied
when cornering under power
(28 %), and another when braking
for a corner (40 %).
Maximum response to minimum effort.
Transmission.

· 49 · · 48 ·
The 911 GT2 |Chassis
The 911 GT2 is fitted with Porsche
Active Suspension Management
(PASM), an electronic damper
adjustment system. This active
damping system offers continuous
adjustment of individual damping
forces based on current road
conditions and driving style.
The driver can choose from two
basic setup modes: ‘Normal’ and
‘Sport’. ‘Normal’ mode is designed
for general road driving and wet
circuit use. ‘Sport’ mode enables
greater lateral acceleration and
increases traction on the race-
track.
In either mode, the system
responds to changing loads by
automatically applying the optimum
rate on each individual damper
from a range of predefined options.Various sensors are used to
monitor the movement of the body
during acceleration, braking and
cornering manoeuvres, as well as
on poor road surfaces. The PASM
control unit then evaluates this
data and modifies the damping
force on each individual wheel in
accordance with the selected
mode. The results are a reduction
in pitch and roll as well as con-
sistent road contact on all four
wheels.
If ‘Sport’ mode is selected using
the PASM button identified by a
damper symbol, the suspension is
set to a harder damper rating that
is specially designed for perform-
ance driving. If the quality of the
road surface falls below a certain
threshold, the system immediatelychanges to a softer rating within
the ‘Sport’ setup range. This
adjustment enhances occupant
comfort as well as traction and
grip. When the road surface
improves, PASM automatically
reverts to the original, harder
rating.
Rebound in ‘Sport’ mode –
damper piston with bypass
valve closedRebound in ‘Normal’ mode –
damper piston with bypass
valve open
Compression in ‘Normal’ mode –
damper piston with bypass
valve open
Compression in ‘Sport’ mode –
damper piston with bypass
valve closed
Redefining ‘normal’.
Porsche Active Suspension Management (PASM).

· 51 · · 50 ·The 911 GT2 |
Chassis
Some things never change,
including driver expectations of
a 911 GT2 : sports-oriented
performance, a direct response
and impressive power.
So Porsche Stability Management
(PSM) has been specially adaptedfor the 911 GT2. In addition to
ABS, the package includes two
automatic driver aids: stability
control (SC) and traction control
(TC).
Stability control (SC), which is
responsible for lateral dynamics,uses a range of sensors to moni-
tor the direction, speed, yaw
velocity (speed of rotation around
the vertical axis) and lateral
acceleration of the car. Using
this information, it is possible to
calculate the actual direction of
travel at any given moment. If thecar begins to oversteer or under-
steer, selective braking is applied
on individual wheels to restore con-
trol in critical driving scenarios.
Traction control (TC), with its
integrated ABD (automatic brake
differential), ASR (anti-slip regula-
tion) and EDC (engine drag-torque
control) functions, is responsible
for the longitudinal dynamics of the
car. Configured for sports-oriented
driving, traction control improveshandling under acceleration on
surfaces with inconsistent grip.
It also prevents the rear from
‘stepping out’ if a wheel loses
traction under full power. The
trigger threshold is relatively high,
which means it is rarely employed
in normal dry conditions.
A unique feature of PSM on
the 911 GT2 is that the control
interventions are delayed and
can be disabled completely in
two stages – for deliberate per-
formance handling.
Stage 1 disables the stability con-
trol (SC) via the ‘SC OFF’ switch in
the centre console. In ‘SC OFF’
mode, the control system does
not intervene if the car goes off-
course in the lateral direction,
which means the throttle can
be used to help steer the car.
Traction control (TC) is still active
in this mode.
Stage 2 disables the traction con-
trol as well via the separate
‘SC+TC OFF’ switch, giving the
driver full command of the vehi-
cle. Another unique feature is the fact that stability control
remains disabled in stages 1 and
2 even when the ABS is required
under braking. Specially develop-
ed for the 911 GT2, this revised
system strategy means the car
can also be enjoyed to maximum
effect on the racetrack.
The anti-lock braking system
(ABS 8.0) is integrated in PSM
and remains active, irrespective
of which settings have been
selected. ABS ensures a relatively
short braking distance and thus
enhanced safety.
It’s good to know who’s in control.
Porsche Stability Management (PSM).