Audi CDSB Specifications
| Engine Model: Audi CDSB |
| Engine Type: 4-cycle 8-cylinder DOHC 32-valve turbocharged liquid-cooled diesel |
| Total Displacement: 256.7 cu.in (4.13 L) |
| Rated Engine Power: 346 Hp (258 kW) at 4000 rpm |
| Fuel System Type: Common rail direct injection |
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The Audi CDSB is a 4.2-liter V8 turbodiesel diesel
engine belonging to the EA896 engine family, a series renowned for its
combination of refined power delivery and high thermodynamic efficiency.
Introduced with the third-generation Audi A8 (D4) in 2009, this engine was
designed to deliver effortless performance befitting a luxury flagship sedan.
Its architecture is a 90-deg V8 configuration, utilizing a compacted graphite
iron (CGI) cylinder block for exceptional rigidity and weight savings.
The CDSB distinguishes itself through its use of two variable geometry
turbochargers (VTG) arranged in a biturbo layout, a chain-driven valvetrain, and
a piezoelectric common rail direct injection system operating at pressures up to
2,000 bar. This sophisticated engineering resulted in an engine that offered the
power of a large-displacement unit with the responsiveness and fuel efficiency
characteristic of modern common rail diesel technology.
The engine was exclusively mated to an eight-speed Tiptronic automatic
transmission, channeling its substantial torque to Audi’s quattro permanent
all-wheel-drive system. Production of the CDSB variant concluded with the end of
the D4 A8 lifecycle, representing a pinnacle of diesel V8 engineering before the
industry’s shift toward electrification.
The Audi CDSB engine produces a maximum power output of 258 kW (351 PS; 346 hp)
achieved at 4,000 rpm. The peak torque figure is a substantial 800 Nm (590
lb-ft), available across a wide plateau from 1,750 rpm to 2,750 rpm. This broad
torque band ensures immediate responsiveness without requiring aggressive
downshifts. The engine’s total displacement is 4,134 cc, achieved through a bore
of 83.0 mm (3.27 in) and a stroke of 95.5 mm (3.76 in).
The compression ratio is set at 16.5:1, a value optimized for cold-start
capability and efficient combustion under high boost pressures. The firing order
is 1-5-4-8-6-3-7-2, a common layout for cross-plane V8 engines that contributes
to the engine’s smooth, even power pulses. The CDSB complies with the Euro 5
emission standard, utilizing a comprehensive after-treatment system including a
diesel particulate filter (DPF) and an oxidation catalytic converter.
The cylinder block is constructed from compacted
graphite iron (CGI), a material offering approximately 75% higher tensile
strength and 45% greater stiffness than conventional grey cast iron, while
maintaining a lower overall weight. This material choice provides a robust
foundation for managing the high mechanical and thermal loads generated by the
bi-turbo charging system and the 2,000-bar injection pressures.
The block features a closed-deck design, where the cylinder bores are fully
supported by the upper surface of the block, enhancing cylinder bore stability
and head gasket sealing under extreme pressure. The 90-deg V-angle is
maintained, and the block is designed to accommodate a forged steel crankshaft
running in five main bearings. Cylinder liners are not used; instead, the bores
are precision-machined directly into the CGI material and finished with a
plateau honing process to optimize oil film retention and reduce friction with
the aluminum alloy pistons.
Each cylinder bank is served by its own aluminum alloy
cross-flow cylinder head. The valvetrain utilizes a dual overhead camshaft
(DOHC) configuration per bank, resulting in four valves per cylinder for a total
of 32 valves. The camshafts are driven by a robust timing chain arrangement. A
primary chain connects the crankshaft to an intermediate shaft, and a secondary
chain drives each cylinder head’s intake and exhaust camshafts.
The camshafts actuate the valves via low-friction roller finger followers. The
valves are arranged with a large included angle to optimize the combustion
chamber shape. The intake valves are produced from high-strength steel, while
the exhaust valves are sodium-filled to facilitate efficient heat dissipation
from the valve head to the stem, a critical requirement given the high exhaust
gas temperatures generated by the VTG turbochargers. The valve seats are made
from a sintered metal alloy for enhanced wear resistance under high thermal
stress.
The fuel system is a third-generation common rail
direct injection system, engineered by Bosch. The high-pressure pump, driven
from the front of the engine by the timing chain, generates rail pressures of up
to 2,000 bar (29,000 psi). This pressure is stored in two stainless steel fuel
rails - one for each cylinder bank - which also act as dampeners to eliminate
pressure pulsations. The injection events are controlled by piezoelectric
injectors, which offer significantly faster response times than traditional
solenoid injectors.
This rapid actuation allows for up to seven separate injection events per
combustion cycle, including pre-injections, main injections, and
post-injections. Pre-injections reduce combustion noise and NOx formation, while
post-injections elevate exhaust gas temperatures to facilitate passive
regeneration of the diesel particulate filter. The system’s precision ensures
complete combustion across the entire operating range, contributing to the
engine’s high specific output and refined acoustic characteristics.
The lubrication system utilizes a variable-displacement
vane-type oil pump. This pump adjusts its output according to engine speed,
load, and oil temperature to reduce parasitic losses and improve fuel economy.
The oil pump is mounted in the front of the engine and driven directly from the
crankshaft. The system capacity for a service fill is 9.5 liters (10.0 US qt).
The engine requires engine oil strictly conforming to Volkswagen oil standard VW
507 00.
This specification mandates a low-ash, mid-SAPS (Sulfated Ash, Phosphorus,
Sulfur) synthetic oil, available in viscosities such as 5W-30 or 0W-30. The
low-ash formulation is critical for the longevity of the diesel particulate
filter, preventing ash accumulation that can lead to clogging and increased
backpressure. The oil circuit includes a full-flow oil cooler, integrated into
the oil filter housing, which uses engine coolant to maintain stable oil
temperatures under high load.
The cooling system is a pressurized, cross-flow design
with a total system capacity of 15.0 liters (15.9 US qt). It utilizes an
electric coolant pump as a secondary component for post-run thermal management,
allowing coolant to circulate through the VTG turbocharger housings after the
engine is switched off to prevent localized overheating and coking of the
bearing assemblies. The primary coolant circulation is driven by a belt-driven
mechanical pump.
The system is designed to maintain optimal operating temperatures for both the
engine block and cylinder heads, with separate circuits ensuring uniform thermal
expansion across the CGI block and aluminum heads. The specified coolant is G13,
a pink, silicate-free, long-life coolant based on glycerin, offering superior
corrosion protection for the aluminum components and the high-temperature diesel
cooling circuit. A large-capacity coolant radiator is supplemented by separate
charge air coolers (intercoolers) for each turbocharger bank to maximize air
density and combustion efficiency.
| Intake and Exhaust Systems |
Intake and Charging: The induction system features two
variable geometry turbochargers (VTG) in a biturbo configuration. Each
turbocharger serves one cylinder bank. The VTG mechanism uses adjustable guide
vanes to vary the flow of exhaust gas onto the turbine wheel, effectively
altering the aspect ratio of the turbocharger. This allows the system to
function as a small, quick-spooling turbo at low engine speeds for immediate
boost response and as a large, high-flow turbo at higher rpms for sustained peak
power. The charge air is routed through two air-to-air intercoolers, one mounted
in each front wheel arch, before entering the intake manifold.
Exhaust System: The exhaust manifolds are integrated into the cylinder heads, a
design that reduces weight, shortens the path to the turbochargers for faster
light-off, and improves thermal management. The system incorporates a
close-coupled oxidation catalytic converter, a diesel particulate filter (DPF)
in the underfloor position, and a NOx storage catalytic converter to meet Euro 5
emissions regulations.
Engine Management: The engine is controlled by a Bosch
EDC 17 (Electronic Diesel Control) engine control unit (ECU). This ECU manages
all critical functions, including fuel injection timing and quantity, VTG vane
position, EGR (exhaust gas recirculation) rate, and throttle valve positioning
for the air system. It receives inputs from multiple sensors, including a
wideband lambda sensor for precise exhaust gas monitoring.
The complete engine assembly, including the alternator,
turbochargers, and intake manifold, has a length of 690 mm (27.2 in), a width of
900 mm (35.4 in), and a height of 760 mm (29.9 in). The dry weight of the
engine, without fluids and ancillary components, is 230 kg (507 lb). The use of
compacted graphite iron for the block contributes to a lower overall mass
compared to a traditional cast-iron V8 of similar displacement, aiding vehicle
weight distribution and agility.
The engine oil and oil filter change interval is
specified at a maximum of 15,000 km (9,300 miles) or one year, whichever occurs
first. A high-quality synthetic oil meeting VW 507 00 is mandatory. The timing
chain is designed for the life of the engine under normal operating conditions;
however, inspection of chain tensioners is recommended during major service
intervals.
The fuel filter should be replaced every 30,000 km (18,600 miles) to protect the
high-pressure fuel system from contamination. The diesel particulate filter
(DPF) is designed for self-regeneration under normal driving conditions; forced
regeneration may be required if short-trip driving is prevalent.
The engine coolant (G13) should be checked at each service and replaced at the
manufacturer-recommended interval of 5 years or 150,000 km (93,000 miles). The
air filter element requires replacement every 60,000 km (37,200 miles), though
more frequent changes may be necessary in dusty environments.
Cylinder Head Bolts: The cylinder head bolts are
tightened using a multi-stage torque-to-yield process. The initial stage
requires a torque of 40 Nm (30 lb-ft). This is followed by a second stage of 80
Nm (59 lb-ft). In the third stage, a further 180-deg angle turn is applied. The
fourth stage specifies an additional 180-deg angle turn, followed by a final
check of the angle tolerances.
Main Bearing Cap Bolts: These bolts are tightened using a torque and angle
method. The initial torque is 50 Nm (37 lb-ft). A subsequent 60-deg angle turn
is applied. A final 60-deg angle turn is then required to secure the bearing
caps.
Connecting Rod Bolts: The connecting rod bolts, which are replaced after every
use due to being torque-to-yield fasteners, are tightened to an initial torque
of 30 Nm (22 lb-ft). A final 90-deg angle turn is then applied to achieve the
correct clamping force.
Camshaft Bearing Cap Bolts: These bolts are tightened to a specified torque of
12 Nm (9 lb-ft) in a defined sequence to prevent warping of the camshaft
carrier.
Flywheel (Drive Plate) Bolts: The bolts securing the flex plate to the
crankshaft are tightened to a torque of 60 Nm (44 lb-ft), followed by a 90-deg
angle turn.
Audi A8 (D4): Model years 2009 to 2014. The engine was
fitted as the 4.2 TDI quattro variant across standard wheelbase models in
various global markets.
Audi A8 L (D4): Model years 2010 to 2014. This long-wheelbase version of the A8
utilized the CDSB engine, providing the same high-performance diesel powertrain
in the extended luxury configuration.
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