928 1977 - 1995
Development of the 928 began in late 1971. Porsche believed that the venerable air-cooled 911 could not continue indefinitely, given ever restricting regulations on noise, emissions, and the crashworthiness of rear-engined cars. Also Porsche saw a need for a car to fill the lucrative, horsepower-driven American market, where half of all their new car sales were being made.
Power plants considered for the 928 project included a V6, but an all-aluminium 4.5 litre, 16-valve SOHC V8, designed by Porsche became the chosen power plant. Using Bosch K Jetronic fuel injection it produced 240Hp. This was the first engine designed specifically to use the K Jet system.
Testing of the various drive train and suspension components was carried out in 911, Mercedes, Opel and Audi bodies. Porsche engineers went to great lengths during this process, as the donor cars sometimes had to be shortened, lengthened or widened to accommodate the 928 drive train and suspension. Later full-scale models and prototypes were given extreme testing in desert tests in Africa, and ice tests in Finland.
At its unveiling at the Geneva motor show in 1977 the car stunned the world and received critical acclaim. The 928 was promptly awarded Car of the Year for its many innovations. Among these were the all aluminium engine block and cylinder heads. The “Weissach Axle" (named after the Porsche R&D centre where it was created), also achieved much praise. The goal of the Weissach axle was to eliminate “lift-off” over steer by allowing the rear suspension to actually adjust itself during cornering and also on hard acceleration. The Weissach axle is one of the most noted features of the 928, and was adapted across the model line-up. The front engined car employed a torque tube and rear mounted transaxle assembly to achieve a near perfect 50/50 weight distribution front to rear.
The 928 was available with the choice of a 3 speed Mercedes Benz sourced automatic transmission or an all Porsche 5 speed manual.
Although they are inexpensive to buy – they cost just as much to repair as they did when they were new, and being older than average it is easy to overspend on a vehicle to bring it up to speed, especially since their lower value often results in less care over the years, service- wise.
928 S 1980 – 1985
Displacement was increased to 4.7 litres and horsepower rose to 300Hp. Along with the horsepower increase came bigger brakes, firmer suspension and spoilers front and rear. The 928 S ran alongside the original 4.5 928 till that car was phased out in 1982.
In 1983 Bosch LH Electronic fuel injection was fitted to the range. Power increased to 310Hp. In England the car was released as a 928 S2, this was not done in Australia. 1984 saw a new 4 speed automatic released, still from Mercedes Benz.
928 S3 1986 1986 in Australia saw the introduction of unleaded petrol. It also saw the release of Porsche’s new pollution friendly engines. The 928 received a heavily revised 4 cam, 32 valve, 5 litre V8, equipped with catalytic converters and lambda control. Unfortunately even with the added displacement, due to the stricter emission controls, power for Australian cars dropped to 288Hp. The new engine was fitted into the same body as previous 928’s; some cars came fitted with larger Brembo fixed callipers, though not all. This car only ran for one year, and was never officially called the S3 outside of the factory.
928 S4 1987 – 1991
1987 saw the first real cosmetic update of the exterior of the 928 in ten years. New front and rear bar covers, and driving lights that mimicked the then new 964. The rear taillights were bigger and the rear profile was changed significantly. These updates brought the car into line with Porsche’s new corporate image. The engine received a new, more compact inlet manifold and power rose to 316Hp.
1989 saw another major change to the inside of the cars, an electronic display in the dash was added, with trip computer and tyre pressure monitoring (RDK). RDK (Ruffen Drukken Kontrol) was another world first for Porsche, it allowed the tyre pressures to be monitored inside the cabin, alerting the driver through a display in the dash if pressure dropped below a set value.
928 GT 1991 - 1992
The sporting 928, was fitted with the 5 speed manual gearbox as opposed to the much more common auto. These cars also received sports seats, a higher red line by 200 RPM and power rose to 326Hp. PSD (Porsche electronic limited Slip Differential) was also fitted. Employing an electric pump and hydraulic fluid, it could vary the amount of pressure exerted on the differential clutch plates, as different driving conditions arose. By sensing the wheel speed difference across the rear axle, PSD could effectively lock the differential to force drive to the non driving wheel.
928 GTS 1992 - 1995
The 928 was nearing the end of its life, sales were down, and Porsche as a company was haemorrhaging money badly. The Boxster was already in the pipeline and it had been decided that the 928 would have to make way. So rather than fade away, the 928 went out with a bang.
Enter the GTS; this became the ultimate 928. Everything that customers had asked for was here. Engine capacity was increased to 5.4 litres and power to 350Hp. The rear guards were flared to allow for bigger rubber to handle that extra power. The range-wide 'Cup One' alloys were fitted to the car, along with sleeker 'Cup' mirrors. A new range of exterior colours were available, and equipment levels were the best yet - to travel in a 928 GTS was to travel in the lap of luxury. Every gadget was there: from trick Blaupunkt stereo, to climate control air conditioning, electric heated seats with memory and cruise control. The last 928 ever to be produced was an automatic GTS, finished in sample Lime Green metallic with sample purple leather interior, with matching purple carpets and dash. A fitting end to a model that personified excess.
Some things to consider
The V8 engine range shares a host of common parts and possible problems. I’ve tried to break them down here to the most common issues that arise. These are very strong engines that provide superb power delivery, and long life. Failures are usually avoidable and in most cases are predictable. However failure in any one of these components can be expensive to fix.
The cam belt once snapped will cause severe engine damage. None of the V8 engines are a “free spinning” engine. The rollers, belt condition and tension should be checked at every service. Replacement of these belts should be carried out at no more than 80,000 km or eight years, which ever arrives first. At this time it is important that the tension and idler rollers be inspected for wear and replaced accordingly. Also the water pump is driven by the back of the cam belt and this too can cause premature belt failure if worn.
In all quad cam engines, 928 S3 and on, the inlet cam shaft is driven by a chain from the exhaust cam shaft. The design is very similar, if not the same as the units used in the four cylinder range, as they were developed around the same time. This chain is tensioned by a unit mounted between the two camshafts, the chain running on two nylon tensioner pads. Porsche does not have any servicing requirements for these items. Unfortunately although owners have been made aware of the need to change cam belts regularly, this chain and tensioner assembly appears to have been ignored. In real life the cam chain starts to stretch and the nylon pads wear down. This causes excessive angle of attack at the base of the sprocket teeth on the camshaft, greatly shortening the life of the cam itself and worst case scenario is that eventually the sprocket teeth become so badly degraded that the cam timing slips and causes serious engine damage. Although it may be possible to change the worn cam chain and tensioner pads before they fail, the wear on the sprockets often requires that the camshafts have to be replaced as well. Due to the V8’s being a lower revving engine, this issue is not as common as on the four cylinders, though it should still be checked periodically.
As these all alloy engines heat up and cool down the continual expansion and contraction compresses and stretches the head gasket till it eventually fails or simply rots away. This is usually noticeable if the car is running hotter than usual or there is an excessive pressure in the top radiator hose. Left unattended these faults can become serious, but a replaced head gasket will last a very long time.
Engine Mounts and Sump Gaskets
Early 928’s use a conventional bonded rubber engine mount with gas filled struts to damp the engines movements. With age, the struts fail and the mounts have to deal with a greater range of movement from the engine and can tear. These torn mounts are harder to detect than the failed hydraulic units, as they are still hold the engine up. This still leaves the engine essentially unsecured, and they should be replaced. The damping struts should be replaced as well.
The engine mounts on 928’s built after 1985 are of the hydraulic or “silent bloc” type. Similar to the 944’s of the era, these eventually leak and collapse. The right hand side usually fails first, as it has to deal with the torque of the engine. This failure is usually most noticeable at start up and idle, going away at higher RPM. An easy way to quickly check the engine mounts is to rev the engine by hand in the engine bay and watch. If the engine rocks left to right, then the mounts still have enough fluid in them to support the engine. If not, then the engine is effectively solidly mounted to the vehicle and the mounts should be replaced.
The replacement of the engine mounts, in either type of mount, necessitates the removal of the front cross member of the car, which also gives you (or your mechanic) free access to the engine sump. The sump gasket on all 928’s is a cork unit and as they age they leak. It is a cost effective repair to replace the gasket at the same time as the mounts. Your driveway will love you for it.