Under the hood of every 1990 Saab beats a 2.0-liter four- cylinder engine which powers the front wheels. The engine has 16-valves, dual overhead camshafts and electronic fuel- injection. In Saab 900, 900S and 9000S models, the engine is naturally-aspirated, in all other models, it is turbocharged. In addition, the engine mounted in 9000 Turbos has Saab's patented Direct Ignition System (Saab DI).
The Saab Direct Ignition System features compact, individual ignition coils for each spark plug and no distributor or high- tension ignition wires. These individual coils supply their spark plugs with 40,000 volts at the moment of ignition, enough to guarantee thorough combustion for good performance, fuel economy and minimal emissions. The lack of any ignition wires carrying more than 12 volts ensures no voltage leaks for smooth running and significantly reduces radio frequency interference. Eliminating the underhood high voltage wires also improves the safety of the working environment for Saab technicians. Replacing the distributor is an electronic control unit which sends a 12-volt signal to the appropriate ignition coil in the prescribed engine firing order. The unit works with the engine management microprocessor to maintain optimum ignition timing without spark detonation.
The Saab DI fires each spark plug only on that cylinder's compression stroke; other systems commonly fire each spark plug uselessly on the exhaust stroke.
In addition, to ensure easy starts, the Saab DI has a multispark function. When the ignition key is first turned, each spark plug subseuently fires about 50 times in a fraction of a second. This cleans and dries the spark plug electrodes to aid starting.
The four spark plugs and their individual ignition coils are encased in a shielded metal container that sits atop the engine between the camshafts. This special container and the cylinder head itself serve to insulate the ignition impulses, preventing any electrical interference.
Increasing the flow of air into and the flow of exhaust gas out of an engine's combustion chambers is basic to improving the engine's performance and efficiency. Saab's engineers are perhaps the most experienced automotive designers in the world in improving the breathing of their engines through the use of turbocharging. An ongoing testbed for Saab's turbocharged engines is the Barber-Saab professional race series: The same basic passenger-car turbo engine found in all 900 and 9000 Turbo models is used to power the 165-mph race cars.
With turbocharging, an exhaust-driven turbine spins a bladed impeller wheel in the engine's intake. This forces more air into the engine, which in turn permits more fuel to be injected, resulting in greater power. The faster the engine runs, the more exhaust it produces and the faster the impeller spins, forcing air into the engine's intake. The amount of air that can be compressed into the engine, or the level of turbo boost, is regulated by a pressure control valve called the wastegate.
However, turbocharging an engine to improve its performance creates its own set of challenges. Routinely, manufacturers of turbocharged engines have lowered compression ratios to prevent detonation when the turbocharger is at full boost. Saab engineers have developed a turbocharging system that offers optimum engine performance -- whether the turbo is at full boost or not.
Thanks to Saab's unique Automatic Performance Control (APC), turbo performance can be kept to a maximum with any fuel quality -- without damaging the engine. In addition, the use of APC allowed Saab to design a turbocharged engine that has a compression ratio of 9.0:1, which is extremely high for a gasoline-powered passenger car turbocharged engine. In fact, the compression ratio of the Saab Turbo is higher than some other manufacturers' naturally-aspirated engines. This means that when the engine is not taking advantage of the turbocharger's boost, its fuel economy and performance is still better than other non-turbocharged engines.
The APC utilizes a microprocessor-controlled solenoid to regulate boost pressure. APC monitors the engine for signs of detonation, and at the onset of knock, the APC system directs the solenoid to the lower boost pressure. The ignition system also has the capacity to retard ignition timing under pressure. APC compensates for all grades of fuel so the engine runs well on any unleaded gasoline with an average octane rating of 87 or higher. Optimum performance is achieved with higher octanes, however.
To further improve throttle response, certain 1990 Saab Turbos are equipped with one of two new turbochargers. The high- performance 900 SPG has a Mitsubishi TE05 whose low-end performance is enhanced by a recalibrated basic pressure setting. The 9000 Turbos are fitted with a new, reduced inertia Garrett T25 turbocharger which offers greater response at lower engine speeds. To improve the performance of all turbocharged Saab models, an intercooler is used to lower the temperature of the compressed intake air before it enters the engine. The lower the air temperature, the more dense the inlet charge and more fuel utilized efficiently. The result is more power. The Saab intercooler is an air-to-air variety and is mounted far forward in the engine compartment.
In addition, Saab utilizes a water-cooled bearing housing to handle the high level of heat that the turbocharger lubrication system must deal with. This helps keep the turbo's lubricating oil temperature down and adds to turbocharger reliability. An engine oil cooler is also incorporated.
All Saabs have 16-valve, dual overhead camshaft engines with a cross-flow, alloy cylinder head. By utilizing two intake and two exhc-_ust valves per cylinder, Saab has optimized the breathing efficiency of its engines over conventional single intake and exhaust valve arrangements. In addition, valve mass is reduced, spark plug placement and combustion chamber shape are optimized. Thanks to the nearly upright position of the four valves and their small faces, the engineers were able to develop a dome-shaped chamber and place the spark plug in its center.
The engine's eight intake and eight exhaust valves are operated directly by two overhead camshafts. The two camshafts are driven by a roller chain with a self tensioner for long life. For added reliability and ease of maintenance, there are self-adjusting hydraulic followers. There is no need to adjust valve lash.
All engines are equipped with electronic fuel injection. This system employs a hot-wire sensor to monitor air mass entering the engine. This information, along with data about engine load and speed, is used by a microprocessor to regulate fuel to the individual injectors. In addition, idle speed is kept constant, regardless of engine load, by its own control system for improved comfort and driving ease.
The microprocessor also controls the ignition system, including the Saab Direct Ignition System on 9000 Turbos, to maintain maximum performance and eliminate detonation, or spark knock. An engine-mounted sensor signals the microprocessor at the first indications of detonation; the electronic control unit then retards ignition timing just enough to avoid the knock. This control strategy is similar to the Automatic Performance Control system fitted to turbocharged engines. The use of the electronically-controlled ignition system also allowed Saab's engineers to extract more performance by designing the naturally-aspirated engine with a high 10.1:1 compression ratio. All Saabs can run on any unleaded gasoline from regular grade, 87 octane, on up although premium fuel is specified for the 900 Turbo SPG.
1990 Saab cars sold in that state (and the western United States) are equipped with electronic exhaust gas recirculation (EGR) systems. Exceptions are the 900 and 900S models, which comply with the standard without the need for EGR.
For 1990, 9000 Turbos are rated at 165 hp at 5,500 rpm and 195 lbs.-ft. of torque at 3,000 rpm. The limited-production 900 SPG is rated at 175 hp at 5,500 rpm and 195 lbs.-ft. of torque at 3,000 rpm, the highest output ever offered on a U.S. Saab model. Other 900 Turbos have 160 hp at 5,500 rpm and 188 lbs.- ft. of torgue at 3,000 rpm.
Naturally-aspirated Saab 9000S models are rated at 130 hp at 5,500 rpm and 128 lbs.-ft. at 3,750 rpm. Saab 900 and 900S models are rated at 128 hp at 6,000 rpm and 128 lbs.-ft. of torque at 3,000 rpm.
All 9000 models are available with either a five-speed manual or four-speed overdrive automatic transaxle. In addition, all 900 series models, with the exception of the 900 SPG, are available with either a five-speed manual or an optional automatic transmission. The SPG is available with a manual transmission only.