Porsche 928 Research Hub

A Replacement for the 911

The story began in 1971. Porsche started planning a replacement for the 911 when everybody thought its days were numbered. There was trend to increasingly stringent emission, safety, and noise standards in the United States and Europe. This led to the idea that the air-cooled/rear-engine concept might not be able to keep pace -- that it could, in effect, be legislated out of existence. All this came together in project goals for a new model that, in the beginning at least, was seen as a 911 replacement.

This new model had to have the quality and performance of previous Porsches and be capable of meeting any and all government regulations that might be conceived in the foreseeable future. The latter meant that a water-cooled engine in front was needed. The new car would also have to be more refined, comfortable, and luxurious than any prior Porsche so as to compete with Mercedes and BMW. And it would have to play well in America, where more than half of all Porsches were sold.

This would be Porsche's first "clean-sheet" road car.

Engine & Chassis

Adding significance to these requirements, this would be Porsche's first "clean-sheet" road car. Porsche decided on a front-engined, V8 power and a more spacious interior that included two real child seats. A 3-speed automatic transmission would be offered beside the standard manual to suit the American market. To obtain the targeted 300 hp output, engineers designed a brand-new 5-liter SOHC V8. Since the engine was quite heavy, they also developed a rear-mounted transaxle gearbox so that even balance between front and rear could be achieved. By 1973, essential development was finished and a prototype was built and under testing. Then the energy crisis hit and sales of large and thirsty cars plummeted which led to the project being put on ice until 1977.

When the 928 was finally unveiled at Geneva motor show that year, its engine was already downsized to 4.5 liters and the resultant output dropped to 240 hp. Despite of running only a single camshaft each bank, the 90-degree V8 was quite advanced in construction. It employed a high-silicon aluminum block, with Nikasil cylinder treatment to reduce friction and save the need of cast-iron liners. Combustion chambers were made oversquare with 95 mm bore and 78.9 mm stroke to ensure smooth revving.

Compression was initially 8.5:1, and Bosch’s reliable K-Jetronic injection fed fuel from a 22.7-gallon plastic tank at the extreme rear. With all this, rated output was 240 DIN horsepower European at 5,500 rpm and 257 pounds/feet of torque peaking at 3,600 rpm. U.S. models arrived with 219 horsepower (SAE net) at 5,250 rpm and 245 pounds/feet of torque (also at 3600) due to a more restricted exhaust system with catalytic converter for emission control (making this a 50-state car from the first) and minor retiming for operation on lead-free fuel.

Apart from the new V8, that car also featured a new invention – Weissach axle, which was a new kind of rear suspension that allowed a certain degree of passive rear-wheel steering. Conventional semi-trailing arm rear suspensions introduced toe-out under braking forces, thus resulted in oversteer. Weissach axle compensated the toe-out thus resulted in a much more neutral and predictable manner. This made the 928 far more secured to drive to the limit than the 911. The double-wishbone front suspensions and new Pirelli P7 low-profile tires also helped it to achieve a roadholding never experienced in any large GTs before.

A front-engine/rear-transaxle layout made as much sense for the posh and potent 928 as it did for the lighter, less powerful 924. And it worked just as well: Front/rear weight distribution ended up a near-perfect 51/49 percent. The standard gearbox was a new Porsche-designed five-speed manual mounted ahead of the differential (not behind, as in the 924), and departing from past practice with a direct topgear ratio (1:1). Alas, it also had a racing-style shift gate like early 911s, with first to the left and down. There was also a three-speed automatic option (to keep the Americans happy). Both transmissions pulled a long-striding 2.75:1 final drive. Power went through a special Fitchel & Sachs twin-disc clutch of fairly small diameter (200 mm/7inches). This was chosen to match the rotary inertia of a thin, rigid driveshaft carried in a torque tube. A helper-spring release kept clutch effort at a manageable 33 pounds. Nowhere was that thoroughness more evident than in the suspension. Geometry looked ordinary but wasn’t. Up front were unequal-length lateral A-arms, with the lower one mounting a concentric shock absorber and coil spring that passed

Although the 928 was by no means lightweight, it employed aluminum bonnet, front fenders and door shells to save weight and by the way improved its weight distribution to a remarkable 51:49. While the body shell looked smooth, its drag coefficient was not quite special at 0.41.

The 928 was designed to have as many Porsche styling points as possible and to be clearly different from other sports cars,” said a 1978 dealer training booklet.

Design & Styling

Design chief Tony Lapine deliberately planned the styling to be futuristic and a little shocking, in line with his notion that if a car looks good right away, it soon starts looking old hat. Never before the world had seen something similar. Its big body shell had the classic sloping back of Porsches but it looked completely modern. It was so round, so smooth, so clean and so refined that today everybody regards it as a timeless design. Bumpers were fully integrated as if part of the body. It did not need to show off muscles or wings to speak of performance. In fact, you can feel its deep reserves of power, solidity and quality from the shape of its sheet metal, incredibly. It was also a rare example of the time that looked truly 3-dimenional, thanks to the symmetric doors, curvy rear quarter windows and the tapered profile of its cross section.

The 928 styling with a fastback was an intentional continuation of Porsche tradition in that it is aerodynamically superior, because of the comparative short front end and a gently tapered and rounded tail, guaranteeing low air turbulence. As well as improving directional stability, the large-surface tail end also meant a large passenger compartment and an outstanding amount of headroom for rear seat passengers in a sports car.

The round headlamps were another classic features of the car – in appearance they looked like ordinary exposed headlamps, but in fact they popped up to operate, like those on Lamborghini Miura. This gave the 928 a certain degree of family resemblance to 911 without looking old-fashioned. The basic Porsche 928 shape unveiled in 1977 stayed with the car through 1995. What people saw was a sleek if rather heavy-looking 2 + 2 hatchback coupe unlike anything else on the road -- a sort of German Corvette.

The Interior

The Porsche 928 cockpit was the most sumptuous yet seen from Porsche, and by the standards of the 1970s, the interior was very stylish.

Its sweeping center console and glovebox area merged smoothly into the cabin to give a modern and airy feel. The instrument pod stood above the dashboard level in a minimalist manner. The early cloth seats were not attractive, but they were soon replaced with good-looking leather buckets – at least most buyers opted.

There was a tilt-adjustable steering wheel that moved the entire instrument cluster with it, thus ensuring good gauge visibility at all times, and air-conditioning that cooled not only the interior but the glove compartment. The rear seats were individual buckets and were good for children, or short adults for short trips. As on previous Porsches, the backrests could be flopped down for extra cargo space. Loading practicality was well taken care by the large tailgate. Between the rear seats was another glove locker, and each door had map pockets concealed beneath armrests that could be pulled in four inches for closer support.

Instrumentation was Porsche-complete, with a large, central speedometer and tachometer flanked by oil pressure/voltmeter and fuel/coolant temperature gauges. A vertical extension of the tunnel console swept up gracefully into the main panel, with a small clock at its base, surmounted by radio, climate controls, and, topmost, a large air vent. Additional vents were located in the upper front portions of the armrests, which also flowed into the dash. R&T complained about the air vents’ meager output but said “the heater, like the 911’s, will practically fry eggs and burn toast.” Left of the center vent was a bevy of warning lights for a central monitoring system. This kept track of all the usual items plus fluid levels, exterior bulb failures, and brake-pad wear. A malfunction illuminated the appropriate lamp, which spelled it out in words (like “wash fluid”), plus a large red master light simply labeled “!”.

Standards features also included a vacuum-operated central locking system, power windows, headlamp washers (activated with the windshield washer when the lights were up and lit), cruise control, a rear-window wiper and wire-element electric defroster, electric remote-adjustable and heated door mirrors, and a four-speaker stereo radio/cassette. The leather trim expanded over the year and eventually included door panels and headliner as the years went by. Buyers could add an extra-cost electric sliding sunroof, limited-slip differential, and factory-fitted burglar alarm.

The 928 was a true (high-end) grand tourer.

Suspension and Handling

Rear suspension on the Porsche 928 was novel. Porsche proudly called it the “Weissach (VEE-sock) Axle,” after the site of the company’s new Development Center not far from Stuttgart. Britain’s Autocar noted that each lower arm “takes braking and acceleration torque loads as well as helping the ball-jointed single top link locate the wheel laterally. The bottom [arm] has its inboard pivot axis inclined outwards at the front, like a semi-trailing arm, to provide a measure of anti-squat. And at the front body pivot, it has a sort of double joint [actually an articulated mount]. The give of this in a corner under braking and decelerating forces [that ordinarily result in] an oversteerinducing toe-out [instead] makes the outside rear wheel toe-in slightly [and] thus counters the usual accidental oversteering self-steer in the case where the driver who has entered a corner too fast lifts off, or, worse, brakes.”

Like so many Porsche innovations, the Weissach Axle was an elegant solution to a thorny problem, and it marked a first for toe-compensating rear suspension in a production car. ZF supplied the 928’s rack-and-pinion steering, which came standard with power-assist. The 928 rolled in on low-profile, high-performance 225/50VR16 Pirelli P7s mounted on special “telephone dial” cast-alloy wheels. These state-of-the-art tires worked with the hightech suspension to give the 928 uncanny cornering stick. The 928 suspension was so remarkably compliant, absorbing most every kind of irregularity, that critics could hardly believe the race-car-like cling in hard driving.