1979 Porsche 928     928 History   ·   928 Technical Information (Porsche History and Tech content on this page provided by and linked to THIS SITE) Body Design With it's flowing, rounded lines the 928 was a car that you either loved or hated at first sight. The Sales Division of Porsche issued a handbook to it's dealerships that advised sales staff on how to field questions on the new 928. The biggest boost for the 928 was being voted "Car of the Year" by European journalists the first year of its production and later, the American journalists had many good reviews. The other selling point was, well, the test drive usually sold the car afterwards. Blue 928 The mostly aluminum body was not just light in weight, but very strong. The roof line of the rounded top and rear had pillars incorporated into the body frame that prevented the roof from collapsing in a roll-over. The rounded shape of the body was specifically designed for strength and rigidity that was a step beyond other vehicles. Extensive wind tunnel testing helped to create the final shape with a somewhat slick .41 drag coefficient. (Remember this was the late 1970's when the 928 was first released) In the later years the redesign of the nose and tail reduced the drag to .34. Crash Testing 928 But the piece de' resistance was the safety built into the 928's body and frame. "Crush Zones" in the nose and tail of the 928 was an achievement of engineering that has yet to be equaled today. Both the polypropylene nose and tail pieces house steel reinforced impact braces. These braces "crumple" under severe impact, creating a "crush" zone that helps to absorb energies that other vehicles would transmit to the passengers in the vehicle. Even the doors, which had improved bracing against side impacts, would "give" to a point. 928 Safety Crush Zones The 928 Engine The 928 was not the first engine that Porsche had designed with a water-cooled V8. Dr. Ferdinand Porsche had helped design a V8 for Daimler-Benz early in the century and in the 1950's had laid out a unit for Studebaker. The V8 engine, though it has been compared to the Mercedes engine, is not the same even though displacement-wise they are similar. The 928 engine is more over-square and there are other differences to set it apart as Porsche. Engine 16-valve But, in 1977 this new engine was as modern as any water-cooled 90 degree V8 at the time. An all aluminum V8 engine with a single overhead camshaft per cylinder bank. Like any American V8, it had hydraulic lifters/tappets to reduce mechanical noise, but most importantly eliminate need for adjustment. The belt-driven cams were angled so that their covers appeared near vertical, giving the V8 an appearance much like that of the 911’s flat six. The high-silicon aluminum alloy engine was made from a process called Reynolds 390 that was used in the 911‘s flat-six engine. General Motors tried it in the Chevy Vega, but working much better in this case. No steel cylinder liners were needed to house the iron coated aluminum pistons because the silicon acted as a wear element. V8 Cutaway-Front/Side View Following a popular design practice, the caps for the five main bearings of the engine are formed into a massive, one piece ladder frame. The block is of an open deck design with generous water-jacket spaces all around the cylinders. Aluminum Engine Components The combustion chamber of each cylinder head was of a hemispherical wedge configuration. Each piston is basically flat on top with small valve cutouts. The engine was designed to be used specifically with the Bosch K-Jetronic fuel injection system. The cleft in the "V" center of the rear six cylinders accommodates the air duct from the injection-metering unit. The spark plugs and injector nozzles are located above the cylinder heads for serviceability. Porsche engineers had made sure that the fuel lines were treated with chrome and then plastic-coated. Joe Rusz of Road & Track asked why Porsche built a simple sohc engine and not an exotic one. Manfred Jantke, Zuffenhausen press officer replied, "A Porsche is not a toy." Finance director Heinz Branitzki added that the engine was designed "with growth potential." We find that out over the 18-year period that the 928 was produced, the engine grew in size and power V8's Being Assembled By Porsche standards the power output of the initial first engines is pretty modest for a 4.5-liter. But combustion was clean and according to Porsche engineers, meeting even the 1978 California emission standards utilizing exhaust gas recirculation, an air pump and catalytic converter. The European cars were rated at a higher horsepower because of less restrictive exhaust systems as compared to the US models. A wet sump oil pump and twin cam belts to the overhead camshafts complete the design. With over-square displacement and 8.5:1 compression the 4.474-liter V8 (273 CID) was conservatively rated by Porsche at: 221 bhp @ 5250 RPM       267 lb./ft @ 3600 RPM Torque In late 1977 the engine started out at 4.5 liters and over the years grew to 5.4 liters by 1994. It had expanded to 4 valves per cylinder over the original 2 valves per cylinder and compression up from 8.5:1 to 10.4:1. The 1993 5.4 liter V8 pumped out a factory rated 345 - 350 HP. Porsche tended to be conservative on the ratings and figures close to 10% Examples: In the early 928's w/the 4.5 liter engine, 221 BHP rating was more in the range of 240 BHP and the factory rating of 137 MPH is close but many cars ran 143-145 MPH in top speed tests.      Early 16-valve Engine                                Later 32-valve Engine 928 Brakes & Suspension Because of the high weight and power of the 928, an exceptional braking system was needed. The braking system itself is fairly conventional. Four large floating-caliper discs are fitted outboard: Large 11.1" ventilated discs in the front and 11.4" in the rear. Twin diagonally split circuits with servo assistance added to the ventilated discs braking power and the split is in conjunction with the negative offset steering. The brake lines were sheathed in copper-nickel iron alloy. The parking brake consisted of a cable to drum setup in the rear wheels, separate from the disc brakes. 928 Cutaway The brakes were more than adequate for the 928 in all driving conditions. They provided outstanding smoothness and stopping power. Initially, the brakes could stop the big 928 at 1G deceleration in 139 feet from 60 MPH, as tested by Road & Track. The brakes were strengthened and improved over time as horsepower and torque also improved, ABS was added in later years on all 928 models. Dual Brake Circuit Diagram The suspension was as advanced as any at the time. Derived from racing, there appears to be nothing unusual about the wishbone and coil setup for front and rear. But, the clever attention to details from the Porsche engineers made the difference that stayed with the 928 in all it's production years. The front suspension is an ordinary one-piece upper wishbone with a T-shaped lower link - similar to the Austin Maxi's - with unequal-length lateral A-arms. An anti-roll bar is standard. The reduce unsprung weight, both wishbones are aluminum. The coil springs encircle telescopic dampers with an anti-roll bar attached to short push rods. The rear wishbone pivots, power-assist rack & pinion steering and engine are all carried on a separate rigid sub-frame. The front suspension geometry uses negative scrub radius to give more stable braking. The rear suspension is similar to the front, a simple lateral link with a wide lower steel wishbone. But the short link through the forward end of the lower radius arm is attached to the vehicle's body. Under braking or cornering forces, the special rubber-bushed link prevents the rear wheels from "toeing out". This device was dubbed the 'Weissach Axle' to mark the achievement of the Weissach Research and Development Center (and pronounced VEE-sock). Weissache Rear Suspension This "toe-in" arrangement helps correct geometry changes when the vehicle is braking during cornering, creating an "oversteer" (or at least a marked reduction in understeer) condition. Like many Porsche innovations, the Weissach Axle was an elegant solution to a thorny problem. It marked a first for toe-compensating rear suspension in a production car. Other manufacturers have devised their own solutions, but it took them a decade to follow Porsche's lead. Rear Axle Corrective Steer Diagram Weissache Rear Axle Toe-In Diagram 928 Drive train The front engine/rear transaxle layout of the 928 makes sense to help provide an almost perfect 51% | 49%-weight distribution. It worked well for the 924 and even better for the Porsche 928. It insured a high polar moment of inertia, reducing nose heaviness and under steer. 928 Cutaway B/W The standard gearbox was a specially designed Porsche 5-speed manual that was mounted ahead of the differential and a direct 1.0:1 direct drive. It had a unique racing-style shift pattern like the early 911’s, with first gear to the left and down, out of normal H pattern shifting. Porsche engineers explained that the V8’s ample torque would permit routine starts in second gear, so first wouldn't be needed that much. Most owners disagreed. Daimler-Benz did provide one major component: The no-extra-cost three-speed automatic transmission. Porsche did design the housing for the auto-transmission. All this went into a 2.75:1 final drive for long stride. Power went through a special Fitchel & Sachs twin-disc clutch of small diameter (200mm/7 inches). This was matched to the thin but rigid drive shaft, which was carried in a torque tube. A helper-spring help keep the clutch effort at 33 pounds. As heavy clutch action is required for GT's, this detail illiterates how thoroughly Porsche engineered the 928. Powertrain Diagram A disadvantage of the 928 is the rotary inertia of the clutch and propeller shaft going into the transmission. The clutch at the rear of the engine attaches to the propeller shaft and the gearbox input pinion at the axle. One or all of these assemblies must be speeded up or slowed down by the synchromesh in the transmission when gears are changed. Rotary inertia is lessened by the use of a slender propeller shaft housed inside a torque tube and suspended by two bearings. Porsche uses a small diameter twin-plate clutch of 7" instead of a larger single plate to reduce rotary inertia. The 5-speed gearbox is an all-new two-shaft unit, with 5th gear being direct drive. The gearbox is situated ahead of the rear axle, powering the differential behind. The differential is not a limited-slip but does drive the rear wheels through a pair of equal-length drive shafts. Final drive ratio was a 2.75:1, in later years the final drive ratio was lowered to 2.27:1. At 60 MPH this meant that instead of 2200 RPM, the engine spun at 1850 RPM with the lower axle ratio. 928 Drivetrain Layout A 3-speed torque converter automatic transmission was offered as an option in the early year models from Daimler-Benz. In later years the transmission was upgraded to a 4-speed automatic that was almost all Porsche. 928 Interior - From Pop-Art to Luxurious On the inside, the car was exotic; with lots of features that one didn't find just anywhere else. Considered as a two-seater, the 928 was roomy with good legroom and headroom. With the rear seats folded down, a large amount of cargo space was available inside the rear glass tailgate. With the rear seats upright, the boot space shrunk to roughly 5 cu. ft. The rear seats were bigger and better than in other Porsche models and even were individual buckets, yet offered little in headroom or legroom for an adult. A large glove storage box was provided between the rear seats. Who else but Porsche would provide sun visors for not just the front, but for rear passengers also? (They made for perfect blinders if the back seat passengers couldn't watch the scenery flash by at 130 MPH). Front Interior Rear Seating For maximum satisfaction, the 928 was designed for its driver. Once sitting down behind the leather bound 3-spoke steering wheel, the driver is in the 928's element. Cabin ergonomics are at a new high for Porsche (in 1978) with the adjustable steering wheel rake (tilt steering) and the instrument panel that moves with it. This was to maintain a constant relationship between the steering wheel, instruments, switches and the driver. Tiltable Steering/Instruments The instruments are mounted behind a single pane of glass that is angled to eliminate reflections. A large speedometer and tachometer are in the center. These are flanked on either side by gauges for water-temperature, fuel level, oil pressure and voltage (battery charge). This was a step up from the flawed 911's arrangement. The heating and ventilation system in the 928 was more than adequate. The 928's controls had a rotary switch for fan speed and two sliders that allowed temperature regulation and distribution of ventilation. Vents were located in the foot wells, beneath the windshield, in the center of the and on the armrests in the doors. Many of these vents could be opened or closed individually. This was a stark contrast to the 911's many scattered sliders that confused most owners and offered little control from hot to cold. Climate Controls Standard features included air conditioning, 4-speaker stereo radio/cassette, cruise control, electric windows and heated door mirrors, rear window defroster, rear window wiper, headlamp washers, a tiny light built into the ignition switch, door armrests that could be extended for extra comfort with hidden compartments below, and even a vanity mirror. Options included a leather interior, electric sliding roof, limited-slip differential and even a factory-fitted burglar alarm. In the later models, the AM/FM/Cassette was replaced with an optional CD player. A cellular phone option was also available from the factory. AM/FM/Cassette The warning light system was something extraordinary. Switch the ignition on, and bright red and green lights appeared as a check that all systems were functioning: Fluids topped off and all exterior lights are working. Any individual warning lights are large and bright to draw the drivers attention. You could turn off the master warning system by pressing a button and it would come on again the next time you switched the ignition on. If the problem is serious, it will not extinguish the warning light until the problem is solved. The loud pop-art check pattern of the seats and door panel cloth inserts was different. But it was found to be overpowering and even horrible to many. The plain leather was offered as an option. In 1980, the leather became standard and the checkered cloth was an option offered at no charge. Later, the cloth checkered inserts were replaced with plain monotone colors that complimented the 928 interior/exterior colors.