The Saab 16 valve engine for everyday motoring marks a new milestone in the development of internal combustion engines. It is a further development of the thoroughly proven, two litre Saab engine, and is equipped with turbocharger, intercooler and the APC system.

The 16 valve engine

An engine with four valves per cylinder makes it possible to achieve more effective combustion of the fuel/air mixture than in conventional engines. This in turn gives lower fuel consumption and increased power.

Engines with four valves per cylinder have long been used to power rally and competition cars - including Saab cars. But the Saab 16 valve engine is not a competition engine designed for the highest possible performance within a narrow range of engine speeds. On the contrary, it is an everyday "workhorse", with good low-speed performance, and has been optimised for the best possible economy, durability and reliability.

Most car manufacturers are developing engines with four valves per cylinder, and this design will probably dominate in the future. But Saab has already accumulated several years of experience in the production of such engines, for economical everyday motoring.

Ideal combustion chamber
The design of the combustion chamber is extremely favourable -it is dome-shaped, with a relatively flat piston crown-which contributes to high efficiency, low knocking tendencies and uniform combustion. The intake manifold is shaped to improve the turbulence in the combustion chamber, and Saab has lodged patent applications for this design. Each of the two pairs of valves has a large flow area, and the engine can thus breathe efficiently. Since the engine has four valves per cylinder instead of two, the individual valves are subjected to far less demanding working conditions. The thermal stresses, for instance, are appreciably lower at a given engine rating than those of an engine with only one intake and one exhaust valve per cylinder.

The four valve arrangement enables the spark plug to be located in the centre of the combustion chamber. So the flame spreads uniformly throughout the combustion chamber. Engine designers describe this as a short and uniform flame path.

In an engine with two valves per cylinder and the spark plug located on one side of the combustion chamber, the flame path is long and asymmetrical. If the temperature at the far end of the combustion chamber is high, the fuel/air mixture may pre -ignite before the flame has reached it, and the engine will then "knock". To avoid such harmful knocking, the compression ratio in this type of engine must be fairly low.

If the engine has four valves per cylinder and the spark plug is located centrally, the compression ratio can be raised without the risk of pre-ignition and knocking. A high compression ratio increases the engine efficiency, enables the engine to use the energy in the fuel more effectively, and raises the engine power, although at a low fuel consumption. The Saab APC system plays an important role in this respect. Using a knock sensor and an electronic control unit, the system continuously monitors the engine load. Due to the APC system, the engine can be run on any grade of fuel between 91 and 98 octane, and the fuel consumption is reduced at the same time.

Self-adjusting, hydraulic cam followers
Since the hydraulic cam followers of the Saab 16 valve engine are self-adjusting, periodic adjustment of the valve clearances is no longer necessary. This simplifies service work and therefore reduces costs. Since the valve clearances are always correct, engine wear will also be reduced. Valve noise will be lower, and the engine will thus run silently and smoothly. Patent applications have been lodged for certain parts of the cam followers.