Fuel And Ignition Systems

Catalytic Converter

Regulated, three-way catalytic converters are standard in Porsche cars beginning with 1990 models. Cars can be ordered with M 150 equipment for delivery with a primary muffler instead of a catalytic converter for countries, in which catalytic converters are not mandatory.

Exhaust System

928 GT and 928 S4 have the same final muffler and twin tailpipe for standardization of parts in 1990 models.

Resonance Intake Distributor

Both engine versions, 928 S4 and 928 GT, have the same intake system beginning with 1990 models. Air Intake Hose

Insulated air intake hoses of Swiss version are installed standard on the engine of 928 GT cars to reduce intake noise.

Engine Control Units

No modifications have been made on the 928 S4 fuel and ignition systems for 1990 models. Modifications on the fuel injection (LH) and ignition (EZK) control units of 928 GT cars are described in the 1989 Model 928 GT Model Information.

Diagnosis - only USA/Canada

Diagnosable control units installed in cars, which are equipped with an airbag system (USA: standard) and for which the airbag control lamp indicates a fault in the system, can be diagnosed with a flashing code tester 9268 only after elimination of the fault in the airbag system and cancellation of the fault memory in the airbag control unit.

3 POWER TRANSMISSION Manual Transmission

G 28/55 Manual Transmission

928 GT is delivered exclusively with a five-speed manual transmission.

A "shorter" final drive ratio is selected in order to have optimal acceleration. Teeth of the final drive are changed to the Kiingelnberg palloid system proven in sport car racing at the same time. Number of final drive teeth:

Pinion 11

Ring Gear 30

Manual transmissions are combined with Porsche's electronically controlled, limited slip differential (PSD), which permits an infinitely variable locking ratio from 0 to 100 %.

Remarks: The transmission diagram shows reference values which are based on a mean effective radius. There is no consideration for slight deviations due to tire tolerances, changes in rolling radius, wear and tire slip.

Automatic Transmission / ATF

A 28/16 Four Speed Automatic Transmission

928 S4 cars are delivered basically with the same A 28/16 automatic transmission from last year without any modifications. Automatic transmissions are also combined with the Porsche limited slip differential (PSD). Components of the electronically controlled transverse lock are identical with those of the G 28/55 manual transmission.

Additional Approvals for DEXRON It D Fluids for A 28 Automatic Transmissions

Folllowing ATF products have been approved for A 28 automatic transmissions in the meantime and can be used for correcting ATF level, replacing ATF and initial filling of repaired or exchanged transmissions.

Make sure that only approved products with the correct, five-digit qualification number (for example: D-21666) are used. Smooth shifting could be impaired considerably when wrong ATF products are used.

B. USA and Canada

Amalie Dexron II D 21594

Castrol Dexron ll/Mercon D-21981 Cltgo Multipurpose ATF D-21571 Exxon ATF (Dexron II, D-21422) Kendall Dexron il-D 21574

Quaker State Dexron II, ATF D-21547

Quaker State Dexron II, ATF (D 21272, 21547)

Unocal Multi-Purpose ATF Dexron II D-22093

Valvoline Automatic Transmission Fluid, Dexron II, D-21270

Amalie Refining Co, Div. of Witco Chemical Corp., Bradford, PA/USA

Castrol Ltd., Swindon/Great Britain

Citgo Petroleum Corp., Tulsa,OA/USA

Exxon Company, Houston, Texas/USA

Kendall Refining Co., Div. of Witco Chemical Corp., Bradford, PA/USA

Quaker State Oil Refining Corporation, Oil City, PA/USA

Quaker State Oil Refining Corporation,Oil City, PA/USA

Unocal Science&Technology Division, Brea, California/USA

Valvoline International, Lexington, Ky/USA

Porsche Limited Slip Differential (PSD)

With Porsche's electronically controlled limited slip differential it is possible to have a locking ratio from 0 to 100 percent depending on dynamic operating requirements. Electronic control is Integrated in the ABS control unit for logistic reasons. A hydraulic slave cylinder on the side of the transmission case is activated by the high pressure hydraulic system depending on requirements. The package of plates in the Porsche limited slip differential, which consists of 20 friction surfaces, is compressed with a force of approximately 3 tons (30 kN) for full locking (100 % locking ratio).

Function of Mechanical Parts

Plate-type limited slip differential (2) and operating components are located in differential case (14). Plate-type locks can be closed (up to 100 % locking ratio) and opened again (0 % locking ratio) for certain operating conditions by slave cylinder (8) which is operated by an external high pressure hydraulic system. Intermediate locking ratios are possible in fractions of a second in infinite steps as required.

Operation

Operating energy is supplied by a hydraulic system with pressure reservoir. Slave cylinder (8) receives pressure and moves the adjustable engaging arm (7) and also engaging bearing (6) in direction of differential case (14).

Force is forward via spring-loaded lever (10), pressure ring (11) and four spring-loaded pressure pins (5) to pressure ring (4), which in turn compresses the plate package (2). This produces friction- type locking between the left output end (1) and differential case (14). Since there is positive lock- ing with the right output end via differential bevel gaers (13), there is also uniform locking effect on the right side.

Pressure in the hydraulic system going to slave cylinder (8) must be reduced or eliminated, when it is necessary to partially or completely eliminate locking in the limited slip differential. This will eliminate or reduce the pressure on plate package (2).

The bevel gear differential can then again function normally with "right to left compensation"

Limited Slip Differential

Car Engine Lip Seal

1 - Output Flange

2 - Regulable plate clutch

3 - Pinion/ring gear set

4 - Pressure ring

5 - Pressure pin with spring

6 - Engaging bearing

7 - Engaging arm

8 - High pressure slave cylinder

9 - Adjusting screw

10 - Spring-loaded lever

11 - Adjusting nut

12 - Pressure ring

13 - Bevel gear differential

14 - Differential case

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