Porsche 928 Design
Though Porsche usually premiered new models at the
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. That may seem an invidious comparison to Porschephiles, but it’s logical, and not just because both cars have V-8s. For example, the 928’s 98.4-inch wheelbase was just 0.4-inch longer than the contemporary Chevy’s. Overall size was broadly similar, too, though the Porsche measured 10 inches shorter (175.7 inches) and offered “+2” seating where the ’Vette did not. Both were obviously high-style, high-performance sports cars, but the 928 was more weight-efficient, tipping the scales at just under 3200 pounds (versus 3500-plus). Undoubtedly, the 928’s fixed-roof unit structure was lighter than the ’Vette’s steel frame and separate fiberglass T-top body.
The basic Porsche 928 shape unveiled in 1977 stayed with the car through 1995.
There was no doubting the efficiency of the 928 engine. It was not, as some thought, an adaptation of the contemporary 4.5-liter Daimler-Benz V-8. Displacement was close enough - 4,474 cubic centimeters versus 4,520 (273 cubic inches versus 276) -- but the Porsche unit was more oversquare with a bore and stroke of 95 ´ 78.9 mm.
Pistons were iron-coated aluminum-alloy units running in linerless bores, made possible by casting the block in Reynolds 390 silicon-and-aluminum alloy, like the 911 engine. Again, the bores were electrochemically etched to leave silicon crystals as the wearing surface. The traditional forged-steel crankshaft ran in five main bearings, with forged connecting rods paired on common journals.
Naturally, there were no Detroit-style pushrods and rocker arms but a single overhead camshaft per cylinder bank, driven by a Gilmer-type belt. Though the banks sat at right angles, their cam covers were situated to make the installed V-8 look much like the 911 flat-six, which was possibly deliberate. The cylinder heads were made of alloy, for additional lightness. 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.
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 top-gear ratio (1:1). Alas, it also had a racing-style shift gate like early 911s, with first to the left and down, out of the normal H. Porsche engineers explained that the V-8’s ample torque permitted routine starts in second gear, so first wouldn’t be needed that much and should thus be “out of the way.” Most owners felt differently.
Daimler-Benz did provide one major component: the no-extra-cost three-speed automatic, wearing a housing designed by Porsche. 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 through the upper arm to an attachment point above. An anti-roll bar was standard.
The 928's water-cooled aluminum twincam V-8 was a engineering tour de force.
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