1998 AUDI S4 Turbo

1415
SSP 198/49

Engine
Engine lubrication
The oil circuit of the 2.7-litre V6 biturbo engine largely corresponds to that
of the 3rd V6 engine generation.
In addition, the two exhaust gas turbochargers are supplied with
pressurised oil from the main oil gallery via a distributor piece. The oil is
returned directly to the oil sump.
The oil cooler was adapted to withstand the higher thermal stresses in
comparison with a naturally aspirated engine.A new feature of the biturbo is
the “integrated oil supply“ (see
next page).
to oil filter/oil cooler
Spring-loaded slipper
(chain tensioner)
Main oil gallery
Oil retention valves
Bypass valve
Filter element
Bearing cap
Oil groove
Oil temperature
sender
Oil pressure switch
Restrictor
Oil retention
valve
distributor piece

The oil circuit
A duocentric oil pump draws in the oil
through a coarse filter. Located in the
pressure chamber of the pump is a
pressure relief valve which protects
downstream components against
pressure peaks during cold starts.
The oil is fed to the oil filter via the oil
cooler. After passing an oil retention
valve, the oil flows through the filter
element. A bypass filter is connected in
parallel with the filter element.
The oil subsequently reaches the main
oil gallery. A branch line is routed to the
oil pressure control valve (clean oil
side).
The following components are supplied
with oil from the main oil gallery:
- the four crankshaft bearings
- the two exhaust gas turbochargers
via an oil distributor line
- the three pairs of piston spray jets via
a spray jet valve
- the cylinder head of cylinder bank 1
via an oil retention valve
The cylinder head of cylinder bank 2 is
supplied through a separate bore from
crankshaft bearing 2 via an oil retention
valve also.
First of all, the camshaft adjustment
valve is supplied with oil from the inlet
drilling in the cylinder head. After the oil
has passed by a restrictor, it is
channeled via the cylinder head main
gallery to the hydraulic valve tappets
and the camshaft bearings.
Exhaust gas turbocharger
Bypass filter
Oil pressure relief valve
from oil filter/oil coolerOil pressure
control valveInduction filter
Oil pressure relief valve
from oil filter/oil cooler
to oil filter/oil cooler

20
Engine
Top view of engine
SSP 198/54

Divert air valve for
turbocharger N249
Injector
Fuel pressure regulator
Solenoid valve for
activated charcoal Solenoid valve for charge
pressure control N75
Camshaft
adjustment valve
N205
Injector
Hall sender G163
Divert air valve
Charge pressure
sender G31
Throttle valve
control part
Camshaft adjustment
valve N208
Divert air valve

21
View of engine from left
SSP 198/53

Injector
Individual ignition coil
Pressure control valve
Prim. catal. converter
Exh. gas turbocharger
Pressure unit for
wastegate flap
Oil cooler
Oil filter
Charge air cooler

22
SSP 198/04

Engine
Air ducting
Fresh air is induced by the combined air filter
and air mass meter and distributed to the two
exhaust gas turbochargers by the air
distributor.
The air distributor is made of plastic.
Advantage:
•
Lower weight
•
The intake air is heated to a lesser degree
by the engine
The air, which is compressed and thus heated
by the exhaust gas turbocharger, is fed to the
charge air coolers.Cooling air intakes in the bumper and air vents
in the wheel housing liners ensure that a
sufficient amount of air flows through the
charge air coolers.
Advantage of charge air cooling:
•
Cooled air has a higher density, and this
means improved volumetric efficiency.
•
The lower temperature reduces knock
tendency also.
The compressed air streams then converge
upstream of the throttle valve control part and
distributed to the individual cylinders in the
intake manifold.
Exhaust gas turbocharger
Throttle valve control part
Charge air cooler
Air distributor
Air mass meter
Air filter

23
SSP 198/32

Charging
Two
water-cooled exhaust gas turbochargers
with wastegate are used for charging.
The charge pressure of both exhaust gas
turbochargers is controlled via the common
charge pressure control valve N75.
Advantages of the biturbo technology:
•
The exhaust gas turbocharger is smaller,
which means better response due its
reduced mass.
•
Higher charge pressure at low engine
speeds.
•
The exhaust gas turbochargers are located
outside the V-angle due to the high
temperatures they reach. This advantage of
this arrangement is that the intake air is not
heated up additionally and the sub-
assemblies are not subjected to so much
thermal stress.
•
Since the turbochargers are flanged
directly onto the exhaust manifold, the
exhaust gases travel less distance and
there is less temperature loss.
•
As a result, the catalytic converters are able
to heat up more quickly and the efficiency
of the exhaust gas turbocharger is
improved by the favourable air-flow.
Intake side of exhaust
gas turbocharger
Charge press. side
of exh. gas turbo-
charger
Exhaust manifold
to exhaust system
Pressure unit for actuating
wastegate flap
Control pressure from
solenoid valve for
charge pressure
control

The turbochargers must be replaced
in pairs
To maintain a synchronous air-flow
through the two chargers, it is
important to observe this instruction
to account for manufacturing
tolerances.
Service personnel are
not
permitted
to adjust the linkage to the wastegate
flap.
Turbine housing
Compressor housing

24
SSP 198/33

Engine
A new generation of probes is used
in this engine.
The “planar lambda probe“ is an
improvement on the finger-type
lambda probe (refer to chapter on
“Sensors”).
Advantage:
•
Short warm-up time
•
Less heating energy demand
•
Long service life
•
More stable control
characteristic
Exhaust system
The exhaust manifolds are designed as pipe
elbows with insulated air gaps.
Advantage:
•
Less heat loss of the exhaust gas and less
heat radiation in the engine compartment
•
Weight saving
Located downstream of each exhaust gas
turbocharger is a primary catalytic converter
close to the engine (metal substrate) .
Advantage
•
The catalytic converters quickly reach a
state of readiness for operation after a cold
start
The large-surface area main catalytic
converters (ceramic substrate) are located
under the vehicle floor.
Lambda probe
Prim. catal. converterMain catalytic converter
Exhaust manifold
Wire mesh ring acting
as a spacer
Air-gap-insulated pipe elbow
Outer shell
Inner pipes

25
SSP 198/31

Pneumatically controlled systems
In the Biturbo, 4 systems are pneumatically
controlled:
•
Charge pressure control
The Motronic ME 7.1 activates the solenoid
valve for charge pressure control N75 and
regulates the charge pressure via the
wastegate.
•
Divert air control in overrun
The Motronic ME 7.1 activates the electric
divert air valve for the turbocharger and
opens the pneumatic divert air valves using
this vacuum.
•
ACF system
The Motronic ME 7.1 activates the solenoid
valve for the activated charcoal canister
and regulates the fuel vapour feed rate to
the engine via the vacuum.
•
Crankcase breather
The crankcase breather controls the return
of oil vapours to the engine via two
mechanical valves.
Solenoid valve for charge
pressure control N75
Solenoid valve for activated
charcoal canister N80
Divert air valve for
turbocharger N249
Non- return valves (ACF system)
Distributor piecePressure control valve
Non-return valve (divert
air control in overrun)
Divert air valve
(pneumatic)

For exact the line routing, please refer
to the Workshop Manual.

26
SSP 198/08

Engine
Charge pressure control
The air mass required to develop a specific
level of torque is determined by means of an air
mass calculation and produced by controlling
the charge pressure as required.
For safety reasons, the engine in the biturbo
regulates the charge pressure, and not the air
mass as is the case with the 1.8-litre 4-cylinder
turbocharged engine.
The charge pressure is measured by charge
pressure sender G31.
The Motronic regulates the charge pressure of
both turbochargers via the solenoid valve for
charge pressure control G31.
If a defect occurs in one of the cylinder banks
(e.g. melting of the catalytic converter or
blockage of the exhaust system), a purely air
mass-oriented charging system would still try
to provide the computed air mass.
This would lead to an excessively high charge
pressure.
In any case, the charge pressure control
prevents an excessively high charge pressure
building up inside the intake system.

Charge pressure sender G31
Atmospheric pressure
Solenoid valve for charge
pressure control N75

Charge pressure
Control pressure