Porsche 928

Early Porsche 928

By the late 1960s, Porsche had firmly established itself as a manufacturer of high-performance sports cars. In the wake of the 1970s oil crisis, executives, including owner Ferdinand Porsche, were beginning to consider adding a more fuel-efficient luxury touring car to the line-up. Managing director Ernst Fuhrmann was pressuring Ferdinand to approve development of the new model due to concerns that the then-current flagship model, the 911, was reaching the limits of its potential. Fuhrmann believed that the future of the company relied upon grand touring cars with conventional engines rather than unconventional sports cars. Slumping sales of the 911 in the mid-1970s seemed to confirm that the model was approaching the end of its economic life cycle. Fuhrmann envisioned the new range-topping grand tourer model as being the best possible combination of a sports coupé and a luxury sedan. This would set it apart from the 911, with its relatively spartan interior and true sports car performance. The targets were that the car had to compete on par with offerings from Mercedes-Benz and BMW while also being successful in the United States, Porsche's main market at the time.

Ordered by Ferdinand Porsche to design a production-feasible concept for the new model, Fuhrmann initiated a design study in 1971, eventually yielding the 928 which was the first clean sheet design by the company for its own model; the 356 was a similar design to the Volkswagen Beetle, the 911 was an evolution of the 356, the 914 was a joint effort intended as a replacement for the Volkswagen Karmann Ghia and 912, and the 924 was the result of abandoned project by Volkswagen and Audi.

Several drivetrain layouts were considered during early development, including rear- and mid-engine, but most were dismissed because of technical and legislative difficulties. Having the engine, transmission, catalytic converter(s) and exhaust all cramped into a small rear engine bay made emission and noise control difficult which were the problems Porsche had with the 911. After deciding that the mid-engine layout did not allow enough room in the passenger compartment, a front-engine, rear-wheel drive layout was chosen.

Porsche engineers wanted a large-displacement engine to power the 928, and prototype units were built with a 5-litre V8 engine rated at 300 PS (220 kW; 300 hp). Ferdinand Piëch proposed the use of a 4.6-litre 90 degree V10 engine with 88 mm bore spacing, a derivative of the Audi 5 cylinder engine (used to power the Lamborghini Gallardo),[8] which in turn is based upon the Volkswagen EA827 unit. The Porsche board objected as this engine would give rise to a rumour of a new 911 with a front-mounted Volkswagen-based engine, but also it is theorized that the board wanted to maintain some distance from the Volkswagen group.

The resulting all-alloy M28 engine has multiple unusual features. Its bore spacing is 122 mm, reflecting the use of thick, all-aluminium cylinder barrels with no steel liners. Water jackets were very large, which indicated that Porsche may have wanted to eventually take this engine racing. In order to maintain a low hood line, the engine was designed for airflow first, thus the spark plugs are located at the top of the head. The four-bolt bearings are sizeable and are fed oil via grooves in the bottom surface of the block. The bearings themselves are supported by a large one-piece structure that forms a lower block, and the cast aluminum oil pan is bolted onto this part.

The oil and water pumps are driven by a timing belt; DOHC engines introduced in 1985 used a hybrid timing system; the timing belt operated only the exhaust camshafts, and the intake camshafts were operated via an internally-mounted simplex roller chain from the exhaust camshaft. This method reduced the complexity of the timing belt layout, and as a result, required fewer components, such as idler rollers and guides, and led to easier and less costly maintenance of the timing belt. This timing system was later used in the Porsche 944, and was also used by Audi and Volkswagen on their belt-driven DOHC engines.

The first two running prototypes of Porsche's M28 V8 used one four-barrel carburetor for initial testing. Actual production cars employed the planned Bosch K-Jetronic fuel injection system. When increasing concern within the company over price and availability of fuel during the oil crisis of the 1970s became an issue of contention, smaller engines were considered in the interest of fuel economy. A push began for the development of a 3.3 L 182 PS (134 kW; 180 hp) powerplant envisioned by Fuhrmann, but company engineers balked at this suggestion. Both sides finally settled on a 4.5 L, SOHC per bank 16-valve V8 rated at 240 PS (180 kW; 240 hp) (219 hp (163 kW) in North America), which they considered to have an acceptable compromise of performance and fuel economy.

The finished car debuted at the 1977 Geneva Motor Show before going on sale later that year as a 1978 model. Although it won early acclaim for its comfort, power and futuristic design, sales were slow. Base prices were much higher than that of the previous range-topping 911 model and the 928's front-engined, water-cooled design alienated many Porsche purists.

Fuhrmann's replacement, Peter Schutz, decided that the models should be sold side by side, feeling that the 911 still had potential in the company's line-up.[9] Legislation against rear-engined vehicles did not materialize. Although it never sold in the numbers Fuhrmann envisioned, the 928 developed an avid following and had an 18-year production run.

Porsche 928 headlights

During its' 18 year production run, the fundamentals of the 928's design remained the same, though the engine and styling underwent several changes, with a distinct ‘facelift’ separating the first generation and second generation cars.

The original 928 design was seen in both 1978 and 1979, with the body lacking both front and rear spoilers. From 1980 (1983 in North America) through 1986, front and rear spoilers were present on "S" and "S2" models, being integrated into the fastback. The first generation cars, which terminated in 1986 with the "S"/"S2" models, all featured a sharper, more angular front end with a distinct 'Shark Nose' profile. From 1987 the overall exterior design was revised and it was this shape that followed the 928 through to final production in 1995. The 1987 redesign integrated the front spoiler into the nose, smoothing out the overall nose profile to fit in with the tastes of contemporary car design & ditching the more angular, shark-nose wedge of the original cars. The rear spoiler became a separate wing rather than an integrated piece and side skirts were also added.[10] The rear tail-light configuration was also different from previous models, with more modern light covers that brought the rear light cluster away from the inset design of the original. GTS models featured flared rear wheel arches to give more room for wider 9-inch wide wheels. Another easily noticeable visual difference between versions is the style of the wheels. Early 928s had 15-inch or 16-inch "phone dial"-style wheels, while most 1980s 928s had 16-inch slotted "flat disc" wheels, with other wheels available as an option. CSs, SEs and 1989 GTs had 16-inch "Club Sport" wheels, later GTs had 16-inch "Design 90" style wheels which were also option on same period S4s (shared with the 944 as well), the GTS used two variations of the 17-inch "CUP" wheels.

The 928 featured a front-mounted and water-cooled V8 engine driving the rear wheels. Originally displacing 4.5 L and featuring a single overhead camshaft design, it was rated at 240 PS (177 kW; 237 hp) in Europe, while smog equipment reduced the output to 219 hp (163 kW; 222 PS) for cars sold in the North American market.[11] The car would first see an increase in both displacement and output for the 1980 model year, with the introduction of the 4.7 L 928 S. The original 16v engine would continue to be developed until its' final iteration in the 1985 model year with the S/S2 model, which produced a 310 PS (228 kW; 306 hp) in European specification, thanks to higher compression, twin distributors with EZK ignition and Bosch LH-Jetronic fuel injection.[12] After 1986 the 16v engine was replaced by the Porsche 32v 5.0 L V8, which Porsche used until the 928 ceased produced in 1995.

In combination with the water-cooled V8 engine, Porsche utilised a transaxle in the 928 to help achieve 50/50 front/rear weight distribution. Performance of early cars were similar to the contemporary 911, despite being heavier. By the time the S/S2 specification was in production, the 928 was outperforming even the 911 Turbo in top speed tests.[13] Early cars came with either a five-speed dog leg manual transmission, or a 3 speed Mercedes-Benz-derived automatic transmission. A four-speed automatic transmission replaced the three-speed option from 1983 in North America and 1984 in other markets. Of cars produced in 1978 and 1979, the majority were fitted with the 5 speed manual gearbox while the optional 3 speed automatic was specified less regularly. This trend quickly reversed as the model continued and final estimates suggest that in excess of 80% of all 928's produced, featured an automatic transmission.[14]

The body, styled by Wolfgang Möbius under the guidance of Anatole Lapine used aluminium for the doors, front wing, front fenders, and bonnet to save weight, while the underlying chassis was made from galvanised steel. It had a substantial luggage area accessed via a large hatchback. Newly developed polyurethane elastic bumpers were integrated into the nose and tail and covered in body-coloured plastic; an advanced feature for the time that aided the car visually and reduced its drag. The distinctive pop-up headlamps, which remained visible in the wings even when they were retracted, completed the 928's shark-like appearance [14] and were based on the units found on the Lamborghini Miura.[15]

Interior from an early car with "Pasha" pattern seat trim

The 928 qualified as a 2+2, having two small seats in the rear. Both rear seats could be folded down to enlarge the luggage area, and both the front and rear seats had sun visors for occupants. The rear seats are small (due to the prominent transmission hump) and have very little leg room; they are only suitable for adults on very short trips or children. The 928 was also the first vehicle in which the instrument cluster moved along with the adjustable steering wheel in order to maintain maximum instrument visibility.

The 928 included several other features such as the "Weissach Axle", a passive rear-wheel steering system that increases stability while braking and during a turn. The engine was notable for its’ unsleeved, silicon alloy engine block made of aluminium, which reduced weight and provided a highly durable cylinder bore.[15]

Porsche's design and development were rewarded during the 1978 European Car of the Year,[16] where the 928 won ahead of the BMW 7 Series, and the Ford Granada. The 928 is the only sports car to have won this accolade.

Porsche 928 GTS

Porsche introduced a refreshed 928 S into the European market in the 1980 model year, although it was the summer of 1982 and MY 1983 before the model reached North America. Externally, the S wore new front and rear spoilers and sported wider wheels and tires than the older variant, but the main change for the 928 S was under the hood, where a revised 4.7 L engine was used. European versions debuted with 221 kW; 296 hp (300 PS), and were upgraded to 228 kW; 306 hp (310 PS) for the 1984 model year. From 1984 to 1986, the S model was called S2 in United Kingdom. These cars used Bosch LH-Jetronic fuel injection system and purely electronic Bosch ignition, the same systems used on the later 32-valve cars. North American-spec 1983 and 1984 S models used among other differences, smaller valves, milder camshafts, smaller diameter intake manifolds, and additional pollution equipment in order to meet emissions regulations, and were limited to 174 kW; 237 PS (234 hp) as a result. Due to low-grade fuel, the 16-valve low compression S engine was made for the Australian market in the 1985 model year. It had a 9.3:1 compression ratio pistons as opposed to the normal 10.4:1 but used the same large intake, high lift cams, large valves, etc. of other S engines.

As the faster European model was not available in the United States and Canada during the first three years of its existence, a "Competition Group" option was created to allow North American customers to have an S model lookalike with front and rear spoilers, 16-inch flat disc wheels, sport seats, sport springs and Bilstein Shock Absorbers. Customers could specify paint and interior colours the same way as on a normal 928. Two cars were made in the late 1980 model year for U.S. with this option. The package was officially available in 1981 and 1982 model years and was canceled in 1983 when the S model became available for these markets. Many cars have had S model features added by subsequent owners, making original "Competition Group" cars difficult to distinguish without checking option codes.

In the 1982 model year, two special models were available for different markets. 202 "Weissach Edition" cars were sold in North America. Unusual features were champagne gold metallic paint, matching brushed gold flat disc wheels, two-tone leather interior, a plaque containing the production number on the dash and the extremely collectible three-piece Porsche luggage set. It's believed these cars were not made with S spoilers even though these were available in U.S. during this time period as part of the "Competition Group" option. The "Weissach Edition" option was also available for the US market 911 for the 1980 model year and 924 for the 1981 model year.

141 special "50th Jubilee" 928 S models were available outside the U.S. and Canada to celebrate the company's 50-year existence as a car manufacturer. This model is also sometimes referred to as the "Ferry Porsche Edition" because his signature was embroidered into the front seats. It featured meteor metallic paint and was fitted with flat disc wheels, wine red leather and special striped fabric seat centers. Similar 911 and 924 specials were also made for world markets.

Porsche updated the North American 928 S for 1985, replacing the 4.7 L SOHC engine with a new 5.0 L DOHC unit sporting four valves per cylinder and producing 215 kW; 292 PS (288 hp). Seats were also updated to a new style, these cars are sometimes unofficially called S3 to distinguish them from 16-valve "S" models. European models kept a 4.7 L engine, which was somewhat more powerful as standard, though lower 9.3:1 compression 32-valve engine together with catalytic converters became an option in some European countries and Australia for 1986. In 1986, revised suspension settings, larger brakes with 4-piston callipers, and a modified exhaust system was available on the 928S, marking the final changes to old body style cars. These were straight from the 928S4, which was to debut a few months later. These changes came starting from VIN 1001, which means that the first thousand 1986 cars had the old brakes, but later cars had this equipment available. This later 1986 model is sometimes referred to as a 19861⁄2 or 1986.5 because of these changes. The name is a little misleading as more than 3/4 of the 1986 production had these updates.

The 928 S4 variant debuted in the second half of 1986 as a 1987 model, an updated version of the 5.0 L V8 for all markets producing 235 kW; 316 hp (320 PS), sporting a new single-disc clutch in manual transmission cars, a larger torque converter in automatic transmission cars and fairly significant styling updates which gave the car a cleaner, sleeker look. S4 was much closer to being a true world car than previous models as the only major differences for North American models were instrumentation in either kilometers or miles, lighting, front and rear bumper shocks, and the availability of catalytic converters in many other markets. The Australian market version was the only one with different horsepower rating at 221 kW; 296 hp (300 PS) due to preparation for possible low grade fuel. Even this was achieved without engine changes.

A Club Sport variant which was up to 100 kg (220 lb) lighter became available to continental Europe and U.S. in 1988. This model was the toned down version of the 1987 factory prototype which had a lightened body. Also in 1987, the factory made five white lightweight S4 models with a manual transmission for racecar drivers who were on their payroll at the time (Derek Bell, Jochen Mass, Hans Stuck, Bob Wollek and Jacky Ickx). These were close to same as later actual Club Sport models and can also be considered prototypes for it. An SE (sometimes called the S4 Sport due to model designation on rear bumper), a sort of halfway point between a normally equipped S4 and the more race-oriented Club Sport, became available for the UK market. It's generally believed that these cars have more power than the usual S4. They utilize parts which later became known as GT pistons, cams and engine ECU programs. Some of them had stronger, short ratio manual transmission. The automatic transmission was not available for this model.

For the 1989 model year, a visible change inside was digital trip computer in the dashboard. At the same time Australian models received the same 235 kW; 316 hp (320 PS) engine management setup as other markets. Porsche debuted the 928 GT in the late winter 1988/89 after dropping the slow-selling CS and SE. In terms of equipment, the GT was like the 928 SE, having more equipment than a Club Sport model but less than a 928 S4 to keep the weight down somewhat. It had the ZF 40% limited-slip differential as standard like the Club Sport and SE before it. Also, like the CS and SE, the GT was only available with a manual gearbox. European 1989 CS and GT wheels had an RDK tire pressure monitoring system as standard, which was also optional for the same year S4. For the 1990 model year Porsche made RDK and a 0-100% variable ratio limited-slip called PSD (Porsche Sperr Differential) standard in both GT and S4 models for all markets. This system is much like the one from the flagship 959 and gives the vehicle even more grip on the track. In 1990, the S4 was no longer available with a manual transmission.

The S4 and GT variants halted production at the end of the 1991 model year, making way for the final version of the 928. The 928 GTS was available for sale in late 1991 as a 1992 model in Europe and in spring of 1992 as an early 1993 model in North America. Changed bodywork, larger front brakes and a new, more powerful 5.4 L, 350 PS (257 kW/345 hp) engine were the big advertised changes; what Porsche wasn't advertising was the price. Loaded GTS models could eclipse US$100,000 in 1995, making them among the most expensive cars on the road at the time. This severely hampered sales despite the model's high competency and long standard equipment list. Porsche discontinued the GTS model that year after shipping only 77 of them to the United States. Total worldwide production for all years was a little over 61,000 cars.

Second-hand models' value decreased as a result of high maintenance costs due to spare parts that are expensive to manufacture. Many parts suppliers and enthusiast networks exist, especially in the United States, Germany and the UK.

Road & Track magazine published a speculative piece in their April 2006 issue regarding the possibility of a new, 928-esque coupé that may debut on a shortened version of the Panamera's platform sometime around 2011 or 2012 model year but this speculation remained uncredible as Porsche denied the possibility of any such model reaching production stage.

The evolution of the 928 during its 18 years of production was quite subtle. The list below show the major differences, which were made to the nose, tail, interior, engine, and wheels.

1978

• Model designation: 928
• Engine displacement: 4.5 L (275 cu in)
• Valves: 16
• Fuel feed: Bosch K-Jetronic fuel injection
• Max. Power (DIN): 240 PS (237 bhp; 177 kW) / 219 bhp (222 PS; 163 kW) (North America)
• Max. Torque: 363 N⋅m (268 lb⋅ft)

1979

• Model designation: 928
• Power: 240 PS (177 kW) / 219 hp (163 kW) (North America)
• Changes:
  • Battery box integrated as part of the body, was previously mounted to gearbox.
  • Gearbox shocks deleted.

1980

• Model designation: 928 / 928 S (only 928 in North America)
• Engine displacement: 4.5 L / 4.7 L (S model only)
• Valves: 16
• Power: 240 PS (177 kW) (4.5) / 300 PS (221 kW) (4.7 S) / 229 HP (167 kW) for North America only.
• Changes:
  • Higher 10.0:1 compression ratio engine (except North America) 4.5 L model. Same power, i.e. 240 PS (177 kW) but more torque, 380 Nm instead of 350 Nm.
  • Bosch L-Jetronic injection in North America.
  • Addition of "S" model, shown at Frankfurt in September 1979.[17] The 928 S was not available in North America until 1983. Front & rear spoilers. Larger brakes.
  • Manual gearbox changed during model year requiring shorter torque tube and different rear subframe.
  • "S" brakes installed during model year except North America.

1981

• Model designation: 928 / 928 S (928 in North America)
• Engine displacement: 4.5 L / 4.7 L (S model only)
• Valves: 16
• Power: 240 PS (177 kW) (4.5) / 300 PS (221 kW) (4.7 S) / 229 HP (167 kW) for North America only.
• Changes:
  • "Competition Package" option available to US market.

1982

• Model designation: 928 / 928 S (928 in North America)
• Engine displacement: 4.5 L / 4.7 L (S model only)
• Valves: 16
• Power: 240 PS (177 kW) (4.5) / 300 PS (221 kW) (4.7 S) / 229 HP (167 kW) for North America only.
• Changes:
  • Vibration damper added to torque tube between 2nd and 3rd support bearing on manual gearbox cars and behind 2nd bearing on automatic gearbox cars.
  • Reverse gear lock added to manual gearbox.
  • 141 "50th Jubilee" 928 S produced for worldwide markets except North America.
  • "S" brakes used in US models.
  • 202 "Weissach Edition" model produced for the US market.
  • 4.5 L model dropped from production at the end of the model year.
  • US "Competition Package" option dropped from production at the end of the model year.

1983

• Model designation: 928 S
• Weight: 1500 kg (3300 lb)
• Engine displacement: 4.7 L
• Power: 300 PS (221 kW) / 234 hp (174 kW) (for North America)
• Changes:
  • North American introduction of "S" model. Standard 928 (4.5 L) model dropped.
  • New style hydraulic motor mounts.
  • Engine shocks deleted at the same time.
  • 4-speed automatic transmission made available for North America.
  • Car body and torque tube changed to accommodate longer gearbox.

1984

• Model designation: 928 S (928 S2 in United Kingdom)
• Weight: 1500 kg (3300 lb)
• Engine displacement: 4.7 L
• Valves: Two per cylinder
• Power: 310 PS (228 kW) / 234 hp (174 kW) for North America.
• Changes:
  • "S" model renamed "S2" in the UK market.
  • Bosch LH-Jetronic injection and 4-speed automatic transmission made available for worldwide markets (previously available in North America only)
  • Torque tube shortened like on U.S. model in the previous year.
  • Bosch EZF ignition system using dual distributors makes debut. This allows higher 10.4:1 compression and increased torque.
  • Compression change done in the middle of model year once 10.0:1 compression ratio resulting piston stock were used up in production.
  • Bosch ABS brakes optional for the first time in a Porsche.
  • At 146 mph (235 km/h) US model top speed, Porsche boldly claims the 928S to be "the fastest street legal production car sold in the US".
  • Important safety related change to front suspension lower ball joints on all cars in September 1983.

1985

• Model designation: 928 S / 928 S2 (UK)
• Weight: 1500 kg (3300 lb)
• Engine displacement: 4.7 L (286 cubic inch)/ 5.0 litre (302 cubic inch) for North America.
• Valves: Two per cylinder (four per cylinder in North America)
• Power: 310 PS (306 hp, 228 kW) (worldwide) / 292 PS (288 hp, 215 kW) (for North America) / 275 PS (272 hp, 202 kW) (4.7 L) for (Australia)
• Changes:
  • New 5.0-litre 288 hp 32-valve engine equipped with Bosch LH-Jetronic injection and Bosch EZF ignition made available for the US market.
  • Top speed (for the US model) is now in excess of 250 km/h (155 mph).
  • Special two-valve 4.7 L engine (9.3:1 c/r) option M151 for Australia. Compression change was done with different shape piston tops. Coupled only with automatic transmission. Engine number is same M28/22 as the high-compression 2-valve engines.
  • LH-Jetronic control box design changed in international markets.
  • New style front seats. Redesigned more modern looking door panels installed when multi speaker stereo was ordered.
  • Gearbox synchromesh changed to BorgWarner design and shorter gear lever, improving driveability on manual transmission cars.
  • Shims left out from front end of torque tube drive plate in automatic transmission cars, this sometimes cause engine thrust bearing failures.
  • Radio antenna moved to embedded windshield wire.

1986

• Model designation: 928 S / 928 S2 (UK)
• Engine displacement: 4.7 L (286 cubic inches) / 5.0 L (302 cubic inches) (North America, optional elsewhere)
• Valves: Two per cylinder (four for North America, optional elsewhere)
• Power: 310 PS (306 hp, 228 kW) (worldwide) / 292 PS (288 hp, 215 kW) (for North America) / 288 PS (284 hp, 212 kW) (for Australia, optional for Germany, Austria, Japan)
• Changes:
  • Lowered 9.3:1 compression ratio four-valve engine optional for some markets along with catalytic converter, standard in Australia. Compression change was done with different shape piston tops.
  • "S4" suspension package and Brembo brakes for 1986 models (from VIN 1001[18] and November 1985 onwards in North America). No U.S. models made with VINs ending between 0938 and 1000 due to parts change.
  • ABS brakes became standard for all markets during model year production.

The M28 V8 engine in a 1987 car

1987

• Model designation: 928 S4
• Weight: 1590 kg (3500 lb)
• Engine displacement: 5.0 L
• Valves: Four per cylinder
• Power: 320 PS (316 hp, 236 kW) / 300 PS (296 hp, 221 kW) for Australia.
• Changes:
  • Different style pistons, cylinder heads, camshafts, intake and larger intake valves compared to earlier 5.0 L engines.
  • Nominal static compression ratio 10.0:1 (True ratio between 9.4:1 and 10.0:1, depending on parts used).
  • Cylinder head studs used in all earlier engines replaced with bolts making it easier to remove heads while engine is in engine bay.
  • Updated LH-Jetronic injection and ignition changed to EZK system, two knock sensors added to engine. Single disk clutch on manual transmission cars, larger torque converter on automatics.
  • Modified front brake calipers used with 2 mm diameter increase for larger pistons. Cars sold to U.S., Canada, Australia and Arab countries got new parts once remaining old design calliper stock was used up.
  • New style front & rear bumpers and rear wing spoiler.
  • Older style S wing still available as option M471. This is the same option number as 1980-82 Competition Group. Porsche has used same numbers several times in different model years and models. In different years they can mean different things.
  • Redesigned front and rear bumper light assemblies.
  • Body changed compared to earlier models to accommodate larger rear lamps, rear seat area modified to give room for new torque converter.
  • Upwards folding rear spoiler and piston oil squirters in engine block on early cars only.
  • Different horsepower rating for Australia due to different ignition map used because of possible low grade fuel.

1988

• Model designation: 928 S4 / 928 CS / 928 SE (UK)
• Engine displacement: 5.0 L
• Valves: Four per cylinder
• Power: 320 PS (316 hp, 236 kW) (S4, CS and SE) / 300 PS (296 hp, 221 kW) (S4) for Australia
• Changes:
  • Lighter 928 CS "Club Sport" version available in Continental Europe and USA, 928 SE (S4 Sport) in UK.
  • Only model year for "CS" (USA) and "SE" (UK). "CS" uses different VIN sequence than normal "S4".
  • Stronger torque tube with 3 mm thicker center shaft for automatic transmission.
  • Pistons with strengthened skirt installed in February 1988.
  • Oil drainage improved in piston skirts.

1989

• Model designation: 928 S4 / 928 CS / 928 GT ("CS" model discontinued in USA)
• Engine displacement: 5.0 L
• Valves: Four per cylinder
• Power: 320 PS (316 hp, 235 kW) (S4 and CS) / 330 PS (326 hp, 243 kW) (GT)
• Changes:
  • February 1989, manual transmission-only "928 GT" debuts as a better-equipped version (all markets).
  • Digital trip computer/warning system added to dashboard, ignition circuit monitor system added.
  • For Australian cars same ignition maps resulting the same horsepower rating as in other markets.
  • North America manual transmission model now uses same shorter final drive ratio as used elsewhere, to simplify production.
  • RDK tire pressure monitoring system optional on S4, standard on CS and GT.
  • Thicker cylinder head casting taken into use early in model year to strengthen head against cracking. Longer head bolts needed because of the change.
  • Modified front brake calipers with improved seals taken into use early in model year.
  • 928 CS now had the same VIN sequence as 928 S4. Model dropped from production during the model year at the end of 1988.

1990

• Model designation: 928 S4 / 928 GT
• Engine displacement: 5.0 L
• Valves: Four per cylinder
• Power: 320 PS (316 hp, 235 kW) (S4) / 330 PS (326 hp, 243 kW) (GT)
• Changes:
  • GT pistons into use in S4 also resulting true 10.0:1 compression ratio for all engines.
  • RDK tire pressure monitoring system standard on all cars. Computer controlled 0-100% PSD locking differential added to both models.
  • S4 no longer available with manual gearbox.
  • Dual airbags now standard across all Porsche models in U.S. Driver's and front passenger airbag optional elsewhere, only driver's side bag available in RHD markets.

1991

• Model designation: 928 S4 / 928 GT
• Engine displacement: 5.0 L
• Valves: Four per cylinder
• Power: 320 PS (316 hp, 235 kW) (S4) / 330 PS (326 hp, 243 kW) (GT)
• Changes:
  • Improvements to cooling in exhaust side at cylinder heads, steering rack, power steering pump, soundproofing, front cooling flaps deleted, new style shift knob with integrated leather booth in manual gearbox cars, etc.
  • Temperature sensors for ignition circuit monitor system moved from #4 and #8 cylinders to #3 and #7 cylinders to improve their efficiency.
  • Check engine warning light added to all US models due to California regulatory demands.
  • Two airbags as standard in LHD models during model year production for most markets.

1992

• Model designation: 928 GTS
• Engine displacement: 5.4 L
• Valves: Four per cylinder
• Power: 350 PS (345 hp, 257 kW)
• Changes:
  • Engine displacement increases to 5.4 L due to increased crankshaft stroke. Piston compression height adjusted to matched new stroke.
  • 10.4:1 compression ratio pistons
  • Milder camshafts for emission purposes
  • Bodywork updated with flared rear fenders and so-called "cup" style wing mirrors.
  • "Big Black" front brakes, significantly larger than the "S4" version.
  • Stronger manual gearbox with differential driven oil pump and front-mounted oil cooler.
  • GTS became available in North America at January 1992 as early 1993 model with later model year VIN. These cars use the same parts as 1992 models and can be differentiated from true 1993 US models with separate VIN sequences and option code M718.

1993

• Model designation: 928 GTS
• Engine displacement: 5.4 L
• Valves: Four per cylinder
• Power: 350 PS (345 hp, 257 kW)
• Changes:
  • Cylinder block lower half studs replaced with bolts.
  • Engine piston rings changed to limit oil consumption and pistons changed to strengthen skirt area.
  • Minor update to gearbox clutch.
  • Air conditioner refrigerant changed to R-134a.
  • Driver-side airbag standard in RHD cars, passenger-side airbag not available in them.

1994

• Model designation: 928 GTS
• Engine displacement: 5.4 L
• Valves: Four per cylinder
• Power: 350 PS (345 hp, 257 kW)
• Changes:
  • Cabin pollen filter added.
  • Dynamic kickdown for automatic transmission models.
  • Wheel design changed to "Cup II", RDK deleted at same time.
  • First 19 US models were made already in spring of 1993, months before when normal model year change occurs in July/August. These M718 option cars still used previous model year parts like Cup I wheels and do not have 1994 model year updates despite using the same 1994 VIN sequence.
  • Connecting rods changed to stronger design part in middle of model year.

1995

• Model designation: 928 GTS
• Engine displacement: 5.4 L
• Valves: Four per cylinder
• Power: 350 PS (345 hp, 257 kW)
• Torque: 500 N·m (369 lb·ft)
• Changes:
  • Special model available in some markets containing 8" wide front wheels.
  • Special colours (only available with automatic gearbox): "Iris blue" metallic and "Aventurine green" metallic colour with Classic grey or Cedar green leather interior.

All production numbers are approximate figures collected from several sources. Porsche hasn't published actual numbers.

^{1) Count contains 2 1980, 458 1981 and 1,084 1982 US "Competition Group" models made.
2) Count contains 202 US "Weissach edition" models made in 1982 model year. 205 is official number which don't seem to be correct. Cars with higher production number than 202 or 205 exist. 217 is known existing plaque number but there were only 202 cars made with M462 option code.
3) Count contains 141 European "50th Jubilee" models made in 1982 model year.
4) Count contains 44 M151 low compression 16V 4.7L S engine models made in 1985 model year for Australian market.
5) Count contains 2,219 so-called S3 US models made in 1985 model year and 877 1986 models made in early part of 1986 model year up to November 1985.
6) Count contains 517 1986 European 32-valve S models. Most were Australian and Japanese models. 266 were optional M298/M299 catalytic converter models sold in Germany, Switzerland and Austria.
7) Count contains 2,071 so-called S3.5 US models made in later part of 1986 model year starting from November 1985.
8) Count contains 6 Club Sport prototypes made in the 1987 model year.
9) Count contains 10 European models and 2 US models made in 1988 model year and 7 European models made in early part of 1989 model year. Last Club Sport cars were made in early winter 1988/89.
10) Count contains 358 European and 115 US/CDN model made in 1989 model year, 808 European and 142 US made in 1990, 516 European and 145 US made in 1991 resulting 1682 European and 396 US model made over two and half year time period. GT production started in around February 1989.
11) Count contains 955 1992, 621 1993, 523 1994 and 399 1995 European models resulting 2,498 cars made. Count contains 88 early VIN 1993, 102 late VIN 1993, 19 + 120 1994 and 77 1995 US models resulting 406 cars made.}

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