The month of classic 900 loving has been extended a little due to all the US 9-3 coverage etc.
This entry continues the publishing of a Saab 900 engineering brochure from the early-mid 1980’s and covers the features of the Saab 2-litre engine and gearboxes.
All Saab 900 models are powered by a liquid-cooled, four-cylinder in-line engine which, with the clutch, gearbox and differential, forms a compact unit of minimum weight and bulk. The arrangement of the inlet and exhaust ports on opposite sides of the cylinder block has given the designers scope for optimizing the cooling of the cylinder head at high engine speeds.
The stroke of the pistons also determines the speed at which an engine can run. In the Saab engine, the stroke is only 3.07 in, and the average piston speeds and inertia forces are moderate even at high engine speeds. This is yet another reason why the Saab 900 can maintain high cruising speeds.
The engine has an overhead camshaft and the valves are therefore operated directly, without push-rods or rocker arms. The camshaft is driven by a chain which is lubricated by oil under pressure. Silent, reliable and maintenance-free. Preheating of the intake air is thermostatically controlled. As the intake air to the engine is always preheated when the ambient air temperature is low, ice formation in the throttle housing is prevented. The preheated intake air also makes the engine run more smoothly when cold.
Click to enlarge.
All Saab engines give excellent performance in relation to fuel consumption. The high torque and the flat torque curve enable the engine to deliver plenty of power even at low speeds, thus eliminating the need for frequent gear changing. The performance of a car should not be measured merely in terms of top speed or acceleration from 0 to 60 mph. Power at low engine speeds, the ability to deliver the power when needed for overtaking and to maintain a high cruising speed, mile after mile, are far more important.
The Turbo engine is a unique Saab innovation. The acceleration and top speed of the Saab Turbo matches that of many cars with six-cylinder or eight-cylinder engines, yet the Turbo does not have the drawbacks inherent in the other engines: large, heavy power units with numerous moving parts and high fuel consumption. Indeed, the Saab turbocharged engine has been referred to by the motoring press as “the engine of the future”.
Fuel injection engine
Mechanical fuel injection. Ensures much more efficient combustion of the fuel under varying driving conditions. The system is very reliable and the engine is easy to start when cold.
Driving performance 900 / 900S
– Acceleration 0-60 mph: ca. 13.5s
(automatic transmission: ca. 17.0s )
– Top speed: ca. 106 mph
(automatic transmission: ca. 100mph)
Turbocharged, fuel-injection engine. The superb performance on overtaking even at low engine speeds – puts the engine in a class of its own. Cruising speeds and maximum speed are also very high.
Driving performance: 900 Turbo
– Acceleration 0-60 mph: ca. 10.5s
(automatic transmission: ca . 15.0s)
– Top speed: ca. 118 mph
(automatic transmission: ca. I l2 mph)
Performance: The 2-liter engine
“….one of the best four cylinder engines anywhere…” (ROAD TEST U.S.A.)
All Saab engines for the U.S. are equipped with the Bosch CI (Continuous Injection) mechanical fuel-injection system, which operates as follows. Fuel is pumped to the fuel distributor which is the brain of the system. The distributor apportions quantities of fuel to the injection valves relative to the amount of air being drawn into the engine.
Click to enlarge.
Inside the fuel distributor is a control piston (6), the position of which is regulated by the arm supporting the measuring disc (7) in the air intake.
The measuring disc moves up and down and adopts a position determined by the speed of the engine and the position of the throttle plate (8). The greater the flow of air, the higher the measuring disc and thus the control piston will be lifted. The control piston has four vertical slots, one for each engine cylinder. As the control piston is lifted, the slots are gradually exposed, allowing a greater quantity of fuel to flow to the spring-loaded injection valves – one for each cylinder. The fuel is injected continuously, once the fuel pressure is high enough. When the engine stops, the pressure in the system fralls and the valve closes again.
During cold-starting, a special valve injects an additional quantity of fuel. The cold-starting valve is controlled by a thermostatic switch. There is also a pressure control regulator, which reduces the pressure above the control piston, allowing it to pass a richer fuel/air mixture. Because the operation of the pressure control regulator is partly governed by engine temperature, the valve performs the same function as the choke on a carburetor engine.
Owing to the ample space in the engine compartment, it has been possible to accommodate a large radiator in the Saab 900. The capacity of the cooling system is sufficient to provide adequate cooling of the engine even when the car is towing a trailer up mountainous roads.
Cooling is controlled by a reliable wax thermostat. To avoid loss of coolant, a separate expansion tank is provided which accepts the extra volume when the coolant expands and returns it as the system cools down.
Thanks to the efficiency of the cooling system, only a fairly small volume of coolant is required, and the engine therefore warms up quickly when starting from cold. Another reason for this is that there is no belt-driven radiator fan which runs continuously. The fan in the Saab 900 is driven by an electric motor, controlled by a thermostatic switch. The fan therefore cuts in automatically only when the engine requires additional cooling, such as when the car is stuck in a traflic jam.
A well dimensioned five speed manual gearbox is standard equipment on all Saabs. The gearbox final drive and differential form an integral unit, with its own lubrication system. The drive shafts have double universal joints, the outer ones being of the Rzeppa type, to provide smooth steering and a positive “feel” to the steering wheel, even when the car is cornering hard. All joints are permanently lubricated.
The primary drive consists of a chain transmission and is silent and reliable. Since the clutch is fitted at the front of the engine, it is adequately cooled and therefore has a long service life. It is also readily accessible for servicing.
Automatic transmission is optional on Saab cars for the U.S. The automatic transmission is made by Borg-Warner. The design has been specially modified for Saab and is integrated with the engine. Drive is through a torque converter and chain transmission to the gearbox and differential.
The automatic control unit is incorporated in the front housing of the gearbox – readily accessible from below. The gearbox has three forward speeds. Transmission of the power to the driven wheels is steady and even, and the car therefore accelerates smoothly. The torque converter enables the car to accelerate briskly even from low speeds, without the need for changing down. The Saab automatic transmission thus has a wide margin of “overlap”, so there is no continual shifting of gears in town traffic, when speeds tend to fluctuate between 15 and 30 mph.
Overriding down-change (kick-down) can be achieved by the driver pressing the accelerator down hard. The automatic transmission is designed to cope with the high power delivered by the Saab 900 Turbo. Combined with the Turbo engine, the new automatic transmission makes for exceptionally smooth driving. The rapidity of the automatic gear changes enables the engine to maintain its charging pressure throughout acceleration.
Exhaust emission control
All Saabs have a breakerless ignition system, which has no moving parts to wear out. The setting of the ignition timing remains unaltered and combustion of the fuel is maintained at maximum efficiency for very long periods before servicing is eventually necessary. This makes for better fuel economy, good performance and cleaner exhaust.
Owing to the strict exhaust emission requirements all Saabs for the U.S. are also fitted with a dashpot (or a fuel shut-off device). Furthermore a lambda system which controls the fuel/air mixture in the engine and a catalyst which removes the unburned hydrocarbons, carbon monoxide and nitric oxides from the exhaust is also fitted. Cars in the U.S. have to run on lead-free gasoline.