A GM Media Release:
Saab’s Technical Heritage: harnessing the power of the turbo
Saab put turbocharging on the automotive map when it pioneered the technology for use in production cars. It is the cornerstone on which Saab has based its powertrain development and remains central to a story of technical innovation and evolution that is still unfolding.
The image of a black, 3-door Saab 99, with its sharp-finned ‘Inca’ alloy wheels and the word ‘turbo’ emblazoned on its flanks and tailgate, has become a long-established motoring icon. Its arrival heralded the dawn of a new era, rewriting conventional wisdom that equated engine power with engine size.
By today’s standards, extracting 145 bhp from a 2.0-liter engine does not sound particularly impressive, but in 1977, when the first turbo model was unveiled, it was regarded as little short of remarkable. Fitting a turbocharger gave 23 per cent more maximum power and a massive 45 per cent increase in torque. To achieve those kind of figures, a naturally-aspirated engine of the time would have been up to 50 per cent larger in capacity and about 50 kg heavier, with overall fuel consumption 30 per cent worse.
Under the impact of higher fuel prices brought about by the first oil crisis of 1973, turbocharging was undoubtedly the right technology at the right time. It gave ‘big’ engine power as and when required, without the downside of continuously high fuel consumption. It is a recipe for enjoyable driving that is just as relevant to the economic climate of today.
While Saab did not invented the turbo – that distinction went to the Swiss engineer Alfred J. Büchi in 1905 – it was the first to car maker to popularize the technique for road car use. Turbocharging and supercharging had, of course, been seen in aero, motor sport and commercial diesel engines, but until the Saab 99 Turbo arrived, turbocharging for cars had been the preserve of a few exclusive, limited run, special models that were an extremely rare sight on public roads anywhere.
It was turbocharging that added a fresh, sporty dimension to the appeal of Saab cars, opening up major global markets by bringing the brand to the attention of a far wider audience. As an acknowledged master of the art, Saab continues to improve and refine turbocharging technology. Advances in engine management systems have given today’s turbo engines a much smoother and more progressive power delivery. And smaller, but faster spinning, turbochargers now respond to the throttle so quickly that the transition from ‘off ‘ to ‘on-boost’ is virtually seamless.
A new era in Saab powertrain development began with turbocharging. Looking back over almost three decades, a series of milestones can be identified along a path that has led to the launch of the new Saab 9-3 Aero 2.8V6 Turbo, the modern day counterpart of that first 99 Turbo.
A Saab-developed wastegate was used to control the build-up of boost pressure on first Saab 99 Turbo. This was a ‘dump’ valve designed to vent some of the exhaust gas if pressure threatened to exceed a safe maximum level, preventing the possibility of stress damage to the structure of the engine. Nowadays, it is a miniaturized by-pass valve in the turbocharger body.
Automatic Performance Control (APC) is announced to protect the engine from harmful premature ignition or ‘knocking’ that was possible due to the wide variations is fuel quality at the time. An acoustic sensor detects the onset of knocking and turbo boost pressure is immediately reduced whenever necessary. The protection offered by APC also gives engineers greater freedom to raise the turbo engine’s compression ratio
A major step forward in power and performance with the introduction of a 16-valve, double overhead camshaft engine replacing the 8-valve, single camshaft arrangement. Improved engine breathing and more efficient dome-shaped combustion chambers help lift power from 145 to 165 bhp (later to 175/185 bhp in ‘Aero’ models) and torque up from 235 to 273 Nm.
Intercooling increases the intake air density to give more power, and better economy, by allowing more fuel to be burnt more effectively. The hot, pressurized charge immediately downstream of the compressor wheel is cooled by passing it through an air-to-air heat exchanger, or mini-radiator.
Saab Direct Ignition system (SDI) introduced. A sold-state cartridge with computerized control and individual spark plug coils replaces the distributor, contact-breakers and HT plug leads. This eliminates all moving parts, providing more reliable performance and allowing much higher voltages for stronger spark generation. Other refinements include the release of a burst of sparks to burn away moisture on the spark plug electrodes if the engine fails to start first time from cold.
The reliability of the latest turbo engines is demonstrated by three standard production 9000 Turbo models during a high speed, non-stop endurance run at the Talladega Speedway in the United States. Stopping only for fuel, servicing and driver changes over 100,000 kms, the lead car averages 213 kph.
Water-cooled turbochargers are introduced, preventing the risk of internal damage through heat-soak. A water jacket around the turbocharger body avoids the possibility of lubricant becoming hot enough to leave burnt deposits on the bearings of the turbo shaft after the engine is switched off.
A light pressure turbocharged engine (LPT) is launched in the 900 model. Operating at a mild 0.45 bar boost pressure, this 145 bhp engine has good torque from under 2,000 rpm without the sharp turn of speed typical of the full-blown engine. It softer, more progressive throttle response appeals to a broader range of customers. The absence of a boost gauge for the first time signifies how Saab now regards the turbocharger as a ‘normal’ engine component.
A 16-valve, DOHC, 2.3-liter turbocharged engine is added to the Saab 9000 range. Featuring counter-rotating balancer shafts for smooth running, this all-new engine delivers 200 bhp and an impressively elevated, flat torque ‘curve’ with an outstanding 330 Nm from just 2,000 rpm.
Saab introduces is own, in-house engine management system, called Trionic. Integrating the control of ignition timing, fuel injection and turbo boost pressure, Trionic supercedes the SDI system. The Saab-written software is among the world’s most sophisticated, utilizing 32-bit processing power capable of two million calculations per seconds.
Trionic uses the spark plugs as ionization sensors by passing a weak current between their electrodes after each ignition in order to measure the quality of combustion. Adjustments are made for each cylinder individually to optimize running efficiency. Electronic throttle control and the measurement of air mass intake volume are further parameters to be added later.
Saab announces the world’s first asymmetrically-turbocharged engine. The turbo is fitted only to the front cylinder bank of a transversely-installed 3.0-liter V6, but delivers its charge to both. The light-pressure turbocharger is extremely small and integrated in the exhaust manifold for efficient packaging. It delivers 30 per cent more torque, which allows high gearing for reduced fuel consumption together with impressive pulling power.
Saab returns to the Talladega Speedway in the United States to set more endurance production car speed records. Covering distances up to 25,000 miles (more than 40,000 km), the lead 900 Turbo maintains an average speed of 226.450 kph.
A new generation of all-aluminum, four cylinder turbo engines is launched in the Saab 9-3 Sport Sedan. The turbocharger is now fitted inboard, behind the transversely-installed engine, to allow quicker warm-up for the front exhaust catalyst and lower cold start emissions. Trionic 8 engine management adds further engine torque and temperature control.
Saab announces the development of a 2.0-liter BioPower turbo engine capable of running on ethanol (E85), a carbon-neutral, renewable energy source, or gasoline in any combination. The engine management system is programmed to automatically accommodate the different ignition timing and fuel/air mixture requirements of ethanol.
An all-new, aluminum 2.8V6 Turbo engine is launched with a single centrally-mounted turbocharger producing 250 bhp and 350 Nm maximum torque between 2,000 and 4,500 rpm. The twin-scroll turbocharger is fed by two inlet tracts, one from each cylinder bank, to separate the exhaust gas pulses, improving gas flow, reducing energy losses and raising efficiency. The engine breathing benefits of variable valve timing are combined with turbocharging for the first time.
Today, the majority of the world’s car manufacturers include turbocharged gasoline engines in their product line-ups. And the promise of ‘big’ engine performance with smaller engine fuel economy continues to attract successive generations of drivers.
The advent of advanced engine control systems has led to levels of operating efficiency beyond the scope of engineers 30 years ago. But nothing has yet been developed to replace the functionality of a turbocharger and Saab’s development work shows that sophisticated technology is providing the key to unlock its full potential.