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Is the Z8 a retro-styled car? "Of course", says Christopher Bangle, BMW's
Chief Designer.
"The classic BMW 507 designed by Graf von Goertz in the '50s was our
reference car," he said. "And since there is only one 507 in the history of the
automobile, built just 252 times, the Z8 is most definitely a retro car. But it is
a retro car full of romantic passion."
BMW has invested a lot of passion and money in pure emotion, focusing
quite deliberately on a classic line.
"Only a car maker with genuine history can create such an homage to a
classic heritage model", said Bangle.
Graf von Goertz' statement that if he were asked to design the 507 of the
year 2000 he would make it exactly like the Z8, confirms Bangle's theory.
"I get that feeling of romantic passion", says Bangle, who regards the
proportions of the Z8 as almost erotic.
"The Z8 is indeed a classic roadster in every respect - a long engine bay,
body lines swinging down at the sides from door level, a sexy derriere and
big wheels."
Not only is the design of the Z8's fascinating body exactly right, so is the
interior.
Bare essentials
"This cockpit intentionally reduced to the essential is meant to create a very
special relationship between the driver and the car", said Bangle. "Our job
was to make you literally feel typical BMW features in this interaction of
sportiness and space".
In practice this means the combination of almost anachronistic design, for
example on the multi-spoke steering wheel, with modern technology such as
the multi-information radio.
Other important design features include the centre mounted instrument
console.
"We deliberately put the instruments of the Z8 right in the middle, enabling
the driver to look straight ahead without being distracted in any way.
"Driving the Z8 is almost like sitting on a motorcycle - you just have the road
ahead of you, enjoying a purist view really unique particularly at night. It's like
flying a small sports plane".
Separate starter button
Another startling retro design feature is the separate starter button.
"Pressing that black button with your thumb you literally feel the power of the
engine - it's a very emotional thing". Said Bangle.
"We also could have made the soft roof of the Z8 disappear behind a flap
when opened. But we didn't want to - our role model was the classic
roadster and classic roadsters have a roof you can see".
Christopher Bangle is firmly convinced that the customers opting for this
kind of car, enjoying the combination of the avant-garde and sporting
performance, want to enter a cockpit completely free of the usual gimmicks.
So to put it in a nutshell, he defines the BMW Z8 as "exactly the same kind of
car the BMW 507 was in its day: the best lifestyle car in the market".
The Body shell and Production of the BMW Z8
From the outset, the type ZO7 prototype exhibited at various motor shows,
offered a clear idea of how the designers of the Z8 interpreted the classic
two-seater sports car.
The concept was to create a car with impressive dimensions on the one
hand, but good handling and nimble behaviour on the other. A car with the
proportions typical of a roadster: a long engine bay, short overhangs front
and rear, and a front air dam extending far down to the road.
The slender, high-rising rear lights, the air scoops at the side, extra-large
wheels and special design features such as neon technology, chrome-plated
rear-view mirrors and tailpipes made of polished steel, clearly
underline the Z8's design philosophy.
Both the power unit as well as the passengers themselves were to be
moved back as far as possible towards the rear third of the car, thus
ensuring optimum traction under all conditions.
BMW's designers and engineers had also given themselves the ambitious
objective to create a car reminiscent in its looks of the legendary BMW 507,
but at the same time to make the Z8 an ideal sports car for everyday
motoring.
Aluminium spaceframe
The first highlight is the use of aluminium spaceframe technology by BMW
for the first time on the body of the Z8.
The entire structure is made up of extrusion-pressed profiles comparable to
the trusses of a timber house. They form the frame, with the body panels
providing the outside skin.
The extrusion-pressed profiles and body panels are held together to form
the overall spaceframe by approximately 1,000 rivets and 57 meters of fused
welding seams (MIG).
This technology offers supreme stiffness in an open sports car, while
guaranteeing excellent behaviour and crash safety.
The structure was also a genuine spearhead in technology, providing BMW
engineers with the opportunity to gain experience working with a new
material.
Crucially, BMW's aluminium spaceframe does not come from a supplier, but
is largely built in-house, providing a wealth of new know-how.
At a special aluminium production shop at the Dingolfing Plant, the pre-processed
extrusion-pressed profiles and the aluminium panels obtained
from suppliers are put together to create the spaceframe.
Dingolfing was the obvious choice for this operation, since BMW already had
an Aluminium Processing Centre here, already manufacturing the hardtop for
the 3 Series convertible and the engine compartment lid for the 7 Series.
An obvious necessity in this development process was to establish a special
quality benchmark, with new quality standards for the process of joining
parts, for the repeated use of standard parts, for the paintwork and surface
treatment.
A further reason for choosing aluminium spaceframe technology was that the
BMW Z8 is being built in a small production series, meaning that a
conventional steel shell structure would not have been economically viable.
Finally, the low weight of aluminium, as well as its resistance to corrosion,
were other important arguments for using this material also on the Z8. As a
result, the Z8 comes with an extremely light body offering supreme torsional
stiffness.
An open sports car with supreme body stiffness
Introducing spaceframe technology on the Z8, BMW is not only launching a
product built of an unusual material, but is also taking a very special
approach in the design and production of the car's entire structure.
The usual approach when building a convertible or roadster is to cut the roof
of a coupé - which usually means a dramatic loss of stiffness and dynamic
body strength. Then this drawback is set off in part through the use of
reinforcements and additional supports and bars bolted on to the car.
BMW's philosophy in creating the Z8 was very different: Instead of the roof
being simply cut off, but rather only lowered a bit from its usual position and
with the roof frames coming closer together at the sides, the roof will
ultimately come to rest on the tunnel between the two seats. This means that
the two roof pillars lead from the middle of the car to the longitudinal
supports front and rear.
The tunnel support is thus able to provide a perfect connection between the
front and the rear end of the car, respectively, and the passenger cell itself,
thanks to the diagonal connection units extending from the side-sills and
tunnel to the longitudinal arms. This superior body stiffness of the Z8 also
makes it possible to keep the side-sills much lower than normal compared
with other cars of this kind.
At the same time this stiffness is the basic precondition for the Z8's nimble
and sporting suspension tuning combined with excellent feedback to the
driver in all dynamic manoeuvres.
On a horizontal plane the diagonal connection between the spaceframe and
the front end of the car by so-called Y-arms is also of great significance. In
principle these arms are made up of two profiles, the engine supports and
the tunnel beams, as well as three structure panels bent round the edges.
The secret is the "Y"
Y-shaped profile units incidentally account for a large share of all the
spaceframe components to be found on the Z8, especially as they connect
perfectly to the 2-D-bent extrusion-pressed profiles. Castings are not used
on the Z8, since casting knodes and junction points would be a weak spot
due to their fracture behaviour.
The advantage of this Y-arm construction on the BMW Z8 is its much better
absorption of impact forces, for example in a crash, transferring such forces
to the middle floor pan far more efficiently than a conventional structure. As
the crash expert would say, such Y-arms fold ideally, since the flow of forces
is either in a straight line or ideally supported on either side.
A further benefit provided by the Z8's package is the superior support of the
longitudinal arms at the rear through an extra-large profile panel, with this
supplementary geometry effectively reducing the number of components.
Compared with other spaceframe structures the Y-arm solution chosen by
BMW at the front and, in a concealed form, at the rear, helps to optimise the
car's structure.
The big advantage for the customer is that the Z8 not only corners more
smoothly and with greater stability, but also offers a significant improvement
of torsional and transverse stiffness.
High standard of crash safety
Compared with the competition, the spaceframe in the Z8 is not only about
30 per cent lighter, but also offers higher characteristic torsional frequency
of a standard otherwise to be found only in cars with a roof.
It is no surprise, therefore, that the Z8 easily passes all of BMW's ambitious
safety tests such as the roof press-in test, the rollover strength test, and the
general operating strength requirements, at the same time naturally fulfilling
all international crash standards.
After the standardised frontal and side collisions as well as the NCAP offset
test with 40 per cent overlap at an impact speed of 64 km/h, the passenger
cell of the BMW Z8 remains completely intact, just as the car easily passes
the EU side impact test at a speed of 50 km/h.
Depending on the severity of an accident, an intelligent airbag system will
activate the frontal and side airbags inside the cockpit of the Z8.
Seat belts with belt force limiters and pyrotechnical belt latch tensioners
ensure not only optimum safety for the two occupants, but also a further
reduction of restraint forces.
Two roll bars fixed in position protect the driver and passenger in the Z8
additionally in the event of a rollover, with the very stable windscreen frame
providing further support.
Three BMW plants work on the Z8
Largely built by hand, the complete front and rear bumpers of the Z8 come
from BMW's Body Equipment Division at the Landshut Plant, as do the sill-and
side window frames again available in all standard and special colours.
Once all these processes have been concluded on the body shell of the Z8,
the car goes to BMW's Munich Plant for final assembly.
A separate area has been set aside at the former Munich Pilot Plant for the
Z8, where operations are not affected by ongoing production of the 3 Series.
All of the job processes the cars go through are located in one single
building, the ready-painted body shell of the Z8 being created here in a total
of 31 job cycles.
Craftsmanship is the name of the game
With the Z8 being a highly exclusive car built in small numbers, the entire
production process is hardly automated. Most jobs are therefore done by
hand, selected associates with years of experience putting the Z8 together.
In this process the associates monitor and record their own work and the
level of quality achieved. Obviously, job processes here are a lot slower than
in large-scale production, the complete assembly and finishing period for the
Z8 being about 10 times as long as for the 3 Series saloon.
The Z8 standard hardtop is made up of aluminium extrusion-pressed
profiles surrounded by foam plastic. With its extremely resistant outer shell,
this sandwich construction allows not only very good insulation, but also
very good stiffness and the reduction of exterior and wind noise to an
absolute minimum.
The Power Unit of the BMW Z8
As befits a thoroughbred sports car, the heart of the BMW Z8 is its high-performance
sports engine created by BMW M and derived from the M5
sports sedan.
Developing exactly 294 kW at 6600 rpm with maximum torque of 500 Nm at
3800 rpm, the quad camshaft V8 engine endows the Z8 with a standard of
dynamic performance unique even in the supreme range of BMW cars.
Supreme power - but smooth and refined
The most fascinating feature of this 8-cylinder power unit is not just the
performance and muscle it has to offer, but rather the way this power is
created.
Particular highlights are the infinite, map-controlled double-VANOS already
well known from BMW's M models, combined in the Z8 with electronically
controlled, drive-by-wire individual throttle butterflies as a centrifugal
lubrication system.
Considered by themselves, the output and torque data of the Z8 power unit
fail to reveal the true character of this exceptional engine. For in developing
this all-aluminium power unit, BMW's engineers focused not just on superior
power and performance, but also on equally superior torque at low engine
speeds.
The result is that 85 per cent of the engine's maximum torque is available
from just 1500 rpm.
The Z8s staggering acceleration and power also result from the free-revving
qualities of the 5.0 litre V8, which will rev smoothly up to 7000 rpm.
Combined with careful gearing and the sporting, short increments of the six-speed
standard gearbox, this means a lot more practical power at virtually
every speed than with an engine revving more slowly and sluggishly.
For example, while the Z8 accelerates brutally to cover the standing-start
kilometre in just 23.5 seconds, acceleration from 80-120 km/h (50-75 mph)
in 4 th gear takes only 4.3 seconds, which is a more useful statistic for normal
motoring.
Crankcase and crankshaft
As on all BMW V8 power units, the crankcase of the Z8 engine is made of
Alusil. The cylinder liners are machine-polished after honing, the cylinder
bores measure 94 mm (3.70") in diameter and the distance between
cylinders is 98 mm (3.86"). The space of only 4 mm remaining between the
cylinders requires special, highly sophisticated metal gaskets on the cylinder
head. Coolant flow, in turn, has been optimised to reflect the supreme power
and performance of the Z8, entering the crankcase at the front and
continuing symmetrically down the two rows of cylinders.
The crankshaft is made of high-strength steel and runs in five bearings. It is
fine-balanced by special heavy metal plugs placed in exactly the right
position. The crankshaft bearings measure 70 mm in diameter and are 22.8
mm wide. The connecting rod bearings, in turn, are 49 mm in diameter and
21 mm across. Axial guidance of the connecting rods is provided by the
large conrod opening.
Connecting rods and pistons
The connecting rods are made by forge cracking and come complete with
rough castings for balancing weight on the large and small conrod openings
with optimum precision.
The pistons feature different-sized valve pockets for the intake and outlet
sides of the engine, giving the Z8 power unit pistons varying in size for the
two rows of cylinders. The top land of the pistons is 6.1 mm high,
compression height is 29.8 mm.
The piston shafts are iron-coated (Ferrostan), the compression ratio is
11.0:1. The pistons themselves are cooled by oil injection jets supplied with
oil through two separate ducts in the crankcase. The jets do not become
active until oil pressure in the engine reaches 2.5 bar.
Cylinder head
The single-piece cylinder head featured in the Z8 power unit is largely the
same as on BMW's other 8-cylinders. Two new features, however, are the
water casing for crossflow cooling and the intake ducts. The gas cycle is
masterminded by two intake and outlet valves on each side; valve drive is by
two overhead camshafts on each row of cylinders. Valve clearance, finally, is
controlled and balanced by maintenance-free hydraulic tappets.
The cylinder gasket is made of three layers of metal incorporating elastic
partitions to separate gas, water (coolant) and engine oil, and to seal off the
entire system from outside. The two outer layers are rubber-coated.
Camshafts and valve drive
The two overhead camshafts on each row of cylinders are made of spherical
graphite castings, the cams themselves being hardened to the requisite
standard by a carefully controlled quenching process while casting, referred
to as hard shell casting. Camshaft drive is provided by a duplex roller chain
extending from the crankshaft to the two intake camshafts. From here a
secondary chain - a simple roller chain - drives the respective outlet
camshaft.
The intake camshafts provide an opening angle of 252 o with lift of 10.32 mm.
The outlet camshafts operate at an angle of 248 o , with 10.2 mm lift.
Both the intake and the outlet valves are carried over in their principle design
from the proven M62 8-cylinder, but are made of even more heat-resistant
material on the outlet side. Shaft diameter of the valves is 6 mm, the intake
valves themselves measuring 35 mm in diameter, the outlet valves 30.5 mm.
Conical valve springs allow engine speeds of 7000 rpm also in the valve
drive system, without jeopardising the engine's endurance and long running
life.
Oil supply
A special, brand-new system serves to supply oil to the Z8 power unit. With
the cylinder heads on a V8 engine being positioned at an angle of 45 o , there
is no natural flow of oil out of the cylinder heads under extreme transverse
acceleration of more than 1g. In such a case, therefore, the only viable
method is to actively extract oil from the cylinder head. And to avoid using
too many extraction pumps due to the frictional losses inevitably involved,
BMW's engineers have developed an entirely new oil supply system.
This system consists of one pressure and two extraction pumps as well as
two electromagnetic switchover valves. As long as the car is driving in a
straight line, oil flowing back from the cylinder heads and the crankshaft
bearings is pumped into the oil sump at the front end of the engine by the
two extraction pumps.
When driving round a bend under significant transverse forces, the solenoid
valves are automatically activated, masterminding the pump extraction
points to ensure that oil is extracted from the oil sump and the cylinder head
on the outer side in each bend. The solenoid valves are activated by the
DSC transverse acceleration sensor also providing this function when the
driver has switched off the DSC system as such.
Thermal oil level sensor
A thermal oil level sensor also monitors the oil level in the oil sump suitably
modified versus the M5 engine, giving the driver a telltale warning in the
instrument cluster should the oil level ever drop below the minimum
required.
The oil change volume is 7.5 litres, oil pressure in the main oil duct is kept at
4 bar. The oil filter is fitted firmly in a separate compartment on the body of
the car, connected by flexible steel pipes to the engine.
An oil/water heat exchanger integrated in the main oil circuit serves to
quickly warm up the engine oil after the engine has been started cold and
prevents the oil temperature from increasing to an excessive level under
high power and at high engine speeds. The heat exchanger is connected to
the flow of coolant directly through the water casing on the first row of
cylinders (cylinders 1-4).
Cooling system
Coolant is fed in equal quantities to the two rows of cylinders by the newly
developed water pump. This consistency is ensured by further refinement of
the coolant ducts through the entire engine, beginning with the design of the
supply ducts leading into the crankcase (cross-flow cooling) and extending
all the way to the outlet cross-sections on the reflow pipes in the cylinder
head.
The supply of water to the individual cylinders can be adjusted by the
openings in the cylinder head gasket. A ring slide thermostat positioned
above the water pump, in turn, ensures a consistent coolant temperature
throughout the entire load and speed range. The coolant pump on the
engine of the BMW Z8 delivers 380 litters (84 Imp gals) of water per minute
at maximum engine speed.
Thanks to the improved heat transition in the radiator, the system provides
greater cooling efficiency than before without an increase in size or
dimensions. The Z8 uses a so-called grooved pipe radiator offering in
particular the advantage of high pressure resistance and a very good heat
transfer. Another new feature is the equalising reservoir ensuring optimum
ventilation of the cooling system when refilled and during operation.
Intake system
Intake air for the engine is drawn in symmetrically through two intake ducts,
flowing through two intake air silencers and two hot-film air mass meters into
the air collector. Due to the V-arrangement of the eight cylinders, the
collector is located above the engine itself.
With the air collector thus being the most prominent design feature in the
engine compartment, particular attention has been given not only to its
perfect function, but also to the design above all of the top cover. Careful
arrangement and configuration of the intake funnels allows a funnel length of
230 mm especially important for the massive torque of the Z8 power unit,
the air collector thus fitting snugly into the limited space available, without
any small diameters exerting a negative effect on engine power.
Fresh air supply is controlled by individual throttle butterflies. Each of these
eight butterflies is housed in a separate casing ensuring play-free
transmission of rotational movements from one to the other throttle butterfly
shaft.
The big advantage of these individual throttle butterflies is that they do not
require a centre bearing, which reduces the opening force when activated
as well as the leakage air rate. The absence of a drive shaft also avoids any
additional elasticity and frictional losses within the system. The air collector
is connected to the throttle butterfly manifolds by a rubber/metal link on
each row of cylinders, separating the collector acoustically and thermally
from the engine itself.
The throttle butterfly shafts are activated by an electronically controlled DC
motor with a layshaft gear fitted in the middle between the two rows of
cylinders and opening the throttle butterflies on cylinders 3 and 6, from
where the remaining butterflies are then operated. Measuring 50 mm or
1.96" in diameter, the throttle butterflies control the cylinder charge and
filling volume.
Depending on running conditions and the engine's operating point, pressure
in the fuel supply system may be up to five bar. The fuel pressure regulator is
fitted directly on the fuel filter from where fuel not required is fed straight
back into the tank. This so-called returnless fuel system offers the particular
advantage of keeping the fuel cool, since there is no return pipe leading into
the tank.
Exhaust system
The exhaust manifold has been carried over directly from the M62 8-cylinder
power unit. A trimetal-coated metal substrate catalyst on each row of
cylinders provides optimum conditions for a high-performance engine of this
calibre, keeping pressure loss to a minimum, ensuring a high standard of
mechanical strength, and allowing a quick response of the catalyst after the
engine has been started cold.
Downstream from the catalyst a crossover link between the two exhaust
pipes separated from one another up to that point allows dynamic
interaction of the exhaust gas flow. This crossover link serves above all to
boost torque at low engine speeds and gives the tailpipes a throaty but
harmonious sound. The interim silencers feature absorption-type damping
technology.
An oxygen sensor upstream and downstream of the catalytic converters
serves to keep the fuel/air mixture at a steady level of lambda = 1, the
downstream sensors also checking the catalytic converters for proper
operation. The two tail silencers, finally, also incorporating absorption
technology, have a total volume of 39.4 litter.
Sound
It almost goes without saying that BMW's sound designers have composed
a very special engine sound for the Z8. The car is audibly full of power,
without becoming unpleasantly loud even on long uphill gradients. Elaborate
optimisation of the sound spectrum focuses above all on low frequencies,
eliminating those disturbing high-frequency sound elements.
Carefully matched to engine load, the unmistakable sound of the BMW Z8
comes out as a deep rumble as long as the driver is cruising in style and
comfort, then increasing to a thrilling crescendo as soon as you start to
push the engine. The obvious impression is one of dynamic performance
and power at all times.
The role model for this sound was once again the BMW 507 lauded over the
decades for the fascinating role of its V8 power unit. Applying the most
advanced methods of sound engineering, BMW's specialists have now
created a perfect sound effect clearly communicated to the outside world by
the twin-chamber exhaust and intake system. And again it goes without
saying that the Z8 complies in full with all sound standards worldwide.
MS S52 engine management
MS S52 engine management is a further development of BMW's own in-house
S50 management system already well known in the BMW M models.
Offering even greater efficiency and higher performance than before, this
new engine management unit serves to control the:
- engine functions
- EBC Electronic Throttle Butterfly Control
- oil circuit functions
- electronic speed limiter (ESL)
- thermal oil level sensor (TOS)
- catalytic converter protection functions
- as well as the two double-VANOS camshaft control system.
Flipping the Sports switch in the cockpit, the driver of the BMW Z8 can opt
for a more sporting or a more comfortable setting of the EBC Electronic
Throttle Butterfly Control, choosing a different gas pedal control map by
means of this electronic function.
EBC Electronic Throttle Butterfly Control
Like the power unit of the BMW M5, the engine of the Z8 also uses
electronic throttle butterfly control commonly known as drive-by-wire. This is
indeed an absolute necessity, since operating the 8 individual throttle
butterflies mechanically by means of a conventional cable would be quite
impossible considering the control forces and the exact dosage required. So
electronic management is certainly the method of choice.
The actuator required for this purpose, a DC motor complete with layshaft
gearing is housed between the two rows of cylinders. The throttle butterflies
of cylinders three and six are driven by pull rods, then activating the other
butterflies accordingly.
This actuator system takes only 120 milliseconds to open the throttle
butterflies. The driver's specific wish for power and performance is then
transferred by two potentiometers in the gas pedal sensor to the MS S52
engine management unit. The optimum throttle butterfly position is
calculated and set by the control unit, the actuator itself being triggered by a
pulse-width-modulated signal in the engine management.
A potentiometer is fitted on the throttle butterfly shafts of cylinders four and
eight in order to monitor the target settings. As soon as this safety concept
determines a deviation of actual from target data, the system is automatically
switched to the failsafe mode allowing the driver to keep on driving his Z8 at
a maximum speed of 100 km/h via the idle speed adjuster.
Double-Variable Camshaft Control (Double-VANOS)
This revolutionary system has already given the BMW M models an
exceptional position in the world market " and now it is also featured in the
new BMW Z8. Compared with simpler versions of camshaft control, double-VANOS
infinitely adjusts the camshaft position throughout the engine's
entire load and speed range, fulfilling the following objectives in the process:
- High torque at low and medium engine speeds
- Internal exhaust gas recirculation at low engine speeds and loads
- Reduction of untreated emissions
- Faster warm-up of the catalytic converter after starting the engine cold
- Reduction in fuel consumption
- Reduction in engine combustion noise
- Less unburned residual gas when idling thanks to the reduction of
valve overlap
- And, as a result, improved, smoother idling
Double-VANOS adjusts not only the intake, but also the outlet camshaft. It
also serves to switch off the engine at its maximum speed of 7000 rpm by
interrupting the ignition and fuel injection.
Comprehensive tests with various camshaft and angle configurations have
served to determine the best adjustment angles on the intake and outlet
camshafts for the Z8 power unit.
Double-VANOS has the task to continuously adjust the intake and outlet
camshafts from "retard" to "advance" and vice versa, valve lift remaining
unchanged in the process.
The double-VANOS operating principle is very logical and straightforward:
The optimum position of the intake and outlet camshafts is determined by
the control unit as a function of the throttle butterfly opening angle and the
speed of the engine. Permanently scanning the pulse wheel position sensors
on the camshafts, the system is able to monitor the relative angle position of
the intake and outlet camshafts, comparing this data with the target required
and if necessary re-adjusting the camshafts immediately by means of
hydraulic control valves.
The actual intervention point is between the timing chain and the camshafts,
a control piston carrying out the adjustment process.
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