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| Turbocharging-the
SAAB way - 1984 |
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Allen White General Manager Saab Car Division
Saab-Scania Australia Pty Ltd.
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,SAAB began the current turbocharging boom
when they released their
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99 series turbo sedan in the Autumn of 1976.
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NEW, ADVANCED ENGINE PROJECT FROM SAAB IN 1984
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THIRD GENERATION TURBOCHARGED ENGINE WITH 16
VALVES
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HAS HIGHER OUTPUT AND LOWER FUEL CONSUMPTION
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At the 53rd International Motor Show in Geneva, Saab will present a new,
advanced engine project, a 2-litre turbocharged engine, featuring a unique method designed
to combine high performance with low fuel consumption.
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The engine has a completely new cylinder head with twin overhead
camshafts and 16 valves, and the turbocharger is controlled by the Saab APC system.
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In its basic design, the new turbocharged engine has been uprated by 10 %
- to 160 hp (118 kW).
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At. the same time, the fuel consumption has been reduced by 10 %.
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The new Saab engine is thus one of the most economical high-performance
engines available today.
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The prototype engine shown in Geneva is also equipped with an
intercooler-, which enables the engine output to be increased further to 180 hp DIN (132
kV/).
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In situations such as when overtaking, the engine can deliver briefly up
to 200 hp DIN (147 kW).
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Simultaneously with the unveiling of the new turbocharged engine, Saab is
launching a broad-based test in which a large number of cars equipped with the new engine
will be used by various drivers in ordinary traffic.
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The experience gained from this test will form the basis for the decision
on when the new turbocharged engine will be taken into serial production.
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Third generation turbocharged engine
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The first version of the Saab 4-cylinder turbocharged engine was
presented in the autumn of 1976. The engine represented an entirely new approach to the
turbocharging of petrol engines for passenger cars. Saab engineers demonstrated that it is
possible to combine low fuel consumption with high performance by applying the
turbocharging principle in a new way. The Saab principle has since been taken up by an
increasing number of engine manufacturers throughout the world.
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Saab presented the second generation turbocharged engine at the beginning
of 1980. This engine featured the Automatic Performance Control (APC) system, for which
patent applications have been lodged and which received numerous awards and citations.
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The APC system allows for maximum utilisation of the energy content of
the fuel and enables the engine to be run on fuels with widely varying octane numbers,
without the need for any adjustments to the engine. At the same time, the APC system
reduces the fuel consumption and improves engine performance.
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Based on the experience gained from more than 80 000 turbocharged petrol
engines, Saab is now presenting a new important advance in this field-. "The -third
generation turbocharged engine", with twin overhead camshafts and 16 valves. The
engine is, of course, also equipped with the Saab APC system which enables it to be run on
fuel with octane numbers ranging between 92 and 98.
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High output - low fuel consumption
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When designing the new engine, the aim was to achieve three main
objectives:
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Reduced fuel consumption Increased performance Reduced service
requirements
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Saab's engine designers have achieved all three objectives by developing
a cylinder head of a completely new design, and patent have been applied for some of the
new features.
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By employing four valves per cylinder and twin overhead camshafts, it has
been possible to position the spark plug centrally above the hemispherical combustion
chamber. This has resulted in more efficient combustion of the fuel-air mixture.
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The principle of four valves per cylinder has so far been fairly uncommon
and has primarily been employed on highly-tuned competition engines. The sole aim was then
to increase the engine output to the maximum attainable.
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By presenting the combination of 16 valves and turbocharqing on an engine
intended for normal motoring, Saab has applied the same philosophy as it did in the design
of the first turbocharged engine in the mid-1970's to use well- known and well-proven
technology - although in an entirely new way.
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The main objective has been to reduce the fuel consumption further and at
the same time increase the engine output.
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In a nutshell, the advantages of the third generation of Saab's
turbocharged engine are a reduction of about 10 % in the fuel consumption and an increase
of 10 % in the engine rating.
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A condition for low fuel consumption is a high compression ratio - 9.O:l
and the Saab APC system which monitors and controls the boost pressure, so that it will
always be at the maximum possible level in relation to the octane rating of the fuel being
used.
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New application of known technology
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- It soon became obvious that we would have to concentrate on the design
of the combustion chamber if we were to achieve the high objectives set up for the fuel
consumption of our turbocharged engines, says Per Gillbrand, who is responsible for the
testing of the new 16-valve engine.
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A modern overhead valve engine with a single overhead camshaft and two
valves per cylinder can be designed so that it is inexpensive to run. Saab has
demonstrated this. with the present turbocharged engine. However, in.order to go a stage
further and reduce the fuel consumption drastically, radical measures had to be adopted
concerning the design of the combustion chamber.
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In an engine with two valves per cylinder and a single overhead camshaft,
the spark plug has to be placed on one side of the combustion chamber, since space
limitations preclude any other locations. As a result, the flame will not advance
completely symmetrically, since the fuel will not be ignited simultaneously in the entire
combustion chamber but can self-ignite (which gives rise to "knocking"). This,
in turn, limits the compression ratio that can safely be used. If the compression ratio
employed is too high, there is risk of non-uniform combustion and consequent dangerous
knocking.
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Another common design consists of twin overhead camshafts and two
inclined valves per cylinder. This arrangement enables the spark plug to be located in the
centre of the combustion chamber. But problems occur with this arrangement too. The two
valves must be of large diameter to enable the engine to "breathe" well; and to
provide sufficient space for the large valves and the spark plug between them the valves
must be inclined at a very steep angle.
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On the other hand, a 4-cylinder turbocharged engine with 16 valves and a
swept volume of about two litres offers excellent opportunities for achieving a high
engine rating and, at the same time, reduced fuel consumption, says Per
Gilibrand.
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Further development of the H engine
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The new 16-valve engine is based on the well-proven Saab type H engine
which, in turn, is a further development of the original 2-litre engine launched in 1972.
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- When designing the type H engine at the end of the 1970s, we already
had our sights set on further development, says Karl-Erik Pettersson, who is responsible
for the design of the new turbocharged engine.
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- The type H engine is very modern in many respects and has provided an
excellent platform for further development. The engine block was designed right from the
start so that it could be used in conjunction with a cylinder head with 16 valves and twin
overhead camshafts.
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Advanced design for the everyday motorist
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Earlier engines with four valves per cylinder and twin overhead camshafts
have often been regarded as complicated and difficult to maintain. This was due to the
fact that these engines were designed to deliver high outputs at high engine speeds, which
has led to heavy demands for regular service. The new Saab 16-valve engine has, on the
contrary,. reduced service requirements since the new cylinder head has been equipped with
hydraulic valve lifters which are completely maintenance-free. The valve clearances in the
engine are thus preset during manufacture. No further adjustments to the valve clearances
are then necessary in conjunction with service.
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Microcomouter controlled fuel injection
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The Saab 16-valve engine has also been equipped with a new type of fuel
injection system - the microcomputer-based electronic LH system from Basch. The LH system
offers numerous advantages:
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Fuel can be metered more accurately under varying conditions, which
contributes to reduced fuel consumption.
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The engine is easier to start - both hot or cold.
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The injection system adjusts itself automatically for different
atmospheric pressures, and this is valuable when the car is driven at high altitudes for
instance.
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The LH system operates at a lower fuel pressure than the earlier system -
3 bar instead of 5.2 bar.
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One of the benefits is reduced risk of leakage.
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The weight has been reduced by 1.5-2 kg.
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The intercooler improves the engine efficiency
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The new engine can be equipped with an intercooler, which is a special
cooler designed to cool the intake air supplied to the engine.
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- A 16-valve turbo engine equipped with an intercooler is the most
efficient engine known to engine designers today, says Per Gillbrand. The intercooler
effectively cools the intake air, which reduces the risk of dangerous knocking. So the
engine can be designed for a high compression ratio, and this automatically leads to low
fuel consumption. The compression ratio of our new engine is 9 . 0 : 1 - which is among
the highest on present-day standard turbocharged engines.
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The Saab intercooler is of new Swedish design and has been developed
specially to enable it to operate satisfactorily even in very cold weather. Earlier
intercoolers were susceptible to freezing and therefore performed unsatisfactorily at very
low temperatures and in damp weather.
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This problem is eliminated on the new Saab intercooler by a special
by-pass valve which., whenever there is risk of freezing, by-passes the intake air past
the cooling element of the intercooler.
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An intercooler also offers the designers full freedom of choice: They can
either optimise the engine for the best possible fuel economy by restricting the engine
rating to about 170 hp, or they can use the intercooler to increase the rating further to
around 180 hp.
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Power boost on overtaking
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The combination of an intercooler and the Saab APC system also provides
an additional power boost, such as in conjunction with overtaking.
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Under normal conditions, the engine runs relatively cool, comfortably
below the conditions likely to give rise to knocking. The APC system utilises this margin
and briefly allows the charging pressure to rise above its normal value. The engine output
thus also increases. A 180 horsepower engine will therefore briefly develop about 200
horsepower, in situations such as when overtaking.
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But this "transient extra power" of about 20 horsepower is
available only for a short period of time. If the temperature in the combustion chamber
will thereafter increase, and so will the tendency towards knocking. The APC system will
then reduce the charging pressure back to the normal level.
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A Saab 900 powered by the 180 hp version of the 16-valve engine has
exceptional performance: the top speed is about 210 km/h and the acceleration is also
appreciably improved.
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160 ho DIN and 8.7 1/100 km
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The engines that will now be included in the Saab broad-based test will
not be equipped with intercoolers and will thus be rated at 160 hp DIN.
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- This output is fully adequate to provide extremely good performance. In
addition, our broad-based test is aimed at evaluating the characteristics of the new
engine under varying conditions, rather that being intended to test the peak performance
of the engine, says Per Gillbrand.
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But there is little doubt that the engine has
enormous development potential.
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- Another aim of the broad-scale tests is to confirm that the fuel
consumption figures we have measured on our test engines can be achieved in real- life
driving with a larger number -of- engines. The 'consumption so far has been exceptionally
low: 8.7 1/.100 km an a mixed cycle (measured according to Swedish Consumer Boards
guidelines). Only a few years ago, a figure as low as this would have been considered
entirely impossible for a high- performance engine of this type.
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A decision on when this engine will be taken into serial production will
be made as soon as the results of the broad-based test have been evaluated.
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During the 1950s, the worlds engine manufacturers abandoned side-valve
engines in favour of overhead valve engines, and this is regarded as a very major step in
the hi-story of engine development- The new engine type now presented by Saab has high
development potential and the indications are that it will be the dominating type of
engine towards the end of the 1980s. They were right - It was.
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Summary
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The '84 third generation of turbocharged engine from Saab has:
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- A cylinder head of cross-f low type, with 16 valves, twin over- head
camshafts and turbocharging with APC.
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- Hydraulic valve lifters, which eliminate the need for valve adjustment.
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- The potential for being modified for different outputs - from 160 hp to
180 hp DIN (118-132 kW).
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- The new., advanced Bosch type LH fuel injection system.
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Technical specification
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Type Turbocharged, 4-cylinder, in-line engine, with cross- flow cylinder
head, twin overhead camshafts and 16 valves.
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Swept volume 1.985 dm3
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Turbocharger Garrett AiResearch T3, with Saab APC system
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Bore/stroke 90/78 mm
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Compression ratio 9. 0: 1
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Engine output 160-180 hp DIN (118-132 kW) at 5.500 r/min, depending an
the design and equipment. (Instantaneously about 200 hp DIN/147 kW).
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Torque 24.5-28 kgf m (240-275 Nm) at 3.000 r/min, depending on the design
and equipmen@
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Fuel consumption Approx. 8.7 11100 km (according to Swedish Consumer
Boards guidelines).
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To ECE standards: Constant 90 km/h 7.1 1/100 km Constant 120 km/h 9.3
1/100 km In city traffic 13.3 1/100 km
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Created by GREG CAMPBELL -
A.T.C.R.
P.O. Box 1050 South Melbourne,
Victoria, AUSTRALIA 3205
SAAB
901
