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Saab 900 Form and Function ..............Performance - Page 10 of 16

"This brochure presents the philosophy and technology behind the various models of the Saab 900. The contents of the brochure are based on the specifications for the 1988 models valid at the time of final editing. The model range, technical specifications and equipment vary from one market to the next."

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Due to the APC system developed by Saab, the turbo engine can extract a maximum amount of energy from any grade of fuel. So the car is more economical on fuel. The APC system also protects the engine against harmful knocking at unsuitable engine loads or a low octane rating of the fuel.	The electronically controlled APC system protects the engine against harmful knocking and ensures optimum utilisation of any grade of fuel between 91 and 98 octane.	The solenoid valve regulates the control pressure to the charging pressure regulator valve which in turn determines the charging pressure.
Saab Turbo with APC Margins must be incorporated in the design of an internal combustion engine to allow for manufacturing tolerances, changes in the condition of the engine and varying climatic conditions. As a result, the energy content of the fuel cannot be utilised fully. The Automatic Performance Control (APC) system is designed to ensure the optimum utilisation of energy in the fuel at all engine speeds. The boost pressure delivered by the turbocharger is continually adjusted to suit the knocking limit of the fuel/air mixture in the cylinders, and fuel of varying octane ratings can therefore be used. The Saab turbo engine with APC can be run on fuel of any grade between 91 and 98 octane, including lead-free fuel. The engine adjusts itself automatically to the fuel used, but the higher the octane rating, the higher the engine power. An advantage of the APC system is that inexpensive, low-octane fuel can be used whenever peak performance is not required.
	The brain of the system is an electronic control unit (1). This recieves signals from 3 sources- from the ignition distributor (2), a knock sensor (3) in the engine block, and a pressure sensor (4) in the intake manifold. As soon as the electronic control unit detects knocking, it will apply a signal across the solenoid valve (5) to the turbo charger to reduce the boost air pressure.

	The thrilling surge of power you feel when the turbo cuts in is a much more telling signal than the smooth sweep of the needle into the yellow field of the boost pressure gauge.	A conventional engine must incorporate risk margins for example, engine tolerances, various climatic conditions and variations in the grade of fuel. An engine equipped with the APC systenm adjusts itself automatically to suit the operating conditions. The energy utilisation will be constantly high at all engine speeds.

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Saab Turbo with APC