A n April 26, 1976, Professor Robert Eberan von Eberhorst gave a lecture on the 100th birthday of the Otto engine at a ceremony of the Association of German Engineers. However, there is not enough space to remember all the highlights of engine construction, said the former head of development in the Auto Union racing department.
Nevertheless, the 74-year-old wanted a “final link in development” in his speech highlight - the 1100 HP CanAm engine from Porsche. 'That was of course a very moving moment,' says Hans Mezger, who was in charge of the 917 project at the time and also designed its twelve-cylinder engine.
The 917 drives everything to the ground
When it first appeared in 1969, the 600 hp twelve-cylinder could barely run for all its power. Shortly thereafter, he narrowly missed victory on the Sarthe due to a gearbox defect; In 1970 and 1971, however, the 917 gave the then still small sports car manufacturer Porsche the first two of so far 16 overall victories in Le Mans as well as the manufacturers' world championship. At the end of the six-kilometer-long Hunaudières, according to the transmission diagram, there were 386 kilometers per hour.
'If you passed the Ferrari,' remembers racing driver Herbert Linge, 'then it took one hit.' Because it drove everything into the ground and couldn't be beaten, the 917 prohibited by the regulations. Porsche did not hesitate for long, equipped the engine with two turbochargers and went into the American CanAm series - a racing formula in which practically everything was allowed and which was dominated by V8 engines with a displacement of up to nine liters and over 800 hp.
In 1972 Porsche won almost all races, in 1973 with the 1100 hp 917/30 without exception all of them. At times, driver Mark Donohue had a lead of over three seconds in pole position. Then the car was banned from the racetrack in America as well.
Of course, the 917 is a total work of art - but the heart of violence is its ingenious drive. “It was clear relatively soon that we would build a twelve-cylinder,” says Hans Mezger of the beginnings of development in June 1968 - after a meeting with the then head of the racing car department, Ferdinand Piëch, and the decision to finally win Le Mans .
The 917 engine is not a boxer engine!
“First we have two construction drawingsput one behind the other by the 911 six-cylinder and saw whether it fits, ”says Mezger. Nevertheless, the popular assertion that the 917 engine is nothing more than two coupled 911 drives or even an eight-cylinder from the 908 extended by four cylinders is simply nonsense: the twelve-cylinder, known internally as the 912, is, unlike the previous drives, one V-engine with a cylinder angle of 180 degrees. On the one hand, this saves installation length because the offset of the left to the right cylinder row now only corresponds to a connecting rod bearing width and not half the cylinder distance or 14 - in addition, the diameter of the connecting rod pin can be slightly reduced with the same load. Since the necessary oil pressure can now also be lower, this, together with the smaller bearings, significantly reduces friction losses.
The secrets of success of the 917-V12
'The oil balance of the twelve-cylinder is exemplary,' explains Mezger, 'it has the best efficiency of all engines built up to that point.' In addition, Mezger minimized the splash losses as much as possible could minimize: While the lubrication points are supplied by a pressure pump, suck Six pumps (two each in the crankcase and one at each end of the two exhaust camshafts) remove the excess oil and pump it back into the dry sump lubrication tank. The low friction and splashing losses are therefore also one of the twelve-cylinder's success secrets.
The other, even more important, is the central output: the drive force is not taken from one end of the crankshaft, but in the middle and transferred to one via a gear Transfer intermediate shaft. 'Tests had shown that the center of the crankshaft represents a vibration node and is absolutely free from torsional vibrations,' explains Mezger.
Additional benefit in addition to the absence of disruptive vibrations: With this design, bothAdd side oil to the crankshaft, which further improves lubrication. It was only logical to use the central output to drive the two overhead camshafts per cylinder row by means of spur gears as well as for the drive shaft of the cooling air fan. This scoops 2,400 liters of air through the cylinders and heads at 8,400 revolutions per second and swallows 17 hp - which corresponds to just three percent of the total output.
The rest of the engine corresponds to typical Porsche virtues: The magnesium housing was sand-cast cast, all twelve cylinders are individually assembled. The two-valve heads, each with two spark plugs, are also individual parts, but are pre-assembled with the camshaft housings to form a shoulder.
New Materials in the test stage
Some of the materials used were completely new at the time: Nikasil liners were used for the first time in racing engine construction for the cylinders, and the connecting rods are made of titanium. 'Back then, nobody in Germany knew how to handle it,' smiles Mezger.
Because the well-known cylinder units of the 908 were initially used, the cubic capacity of the first engines added up to 4.5 liters. “We calculated an output of 520 hp for this - in fact, after two days on the test bench, we already had 540 hp,” reports Mezger. After further test bench meetings and adjustments to the twelve-piston injection system, the test bench finally showed 580 hp; the later version, which grew to five liters due to the larger bore and longer stroke, produced 630 hp. Enough to scare the competition.
Nothing ever went wrong in races
Interesting appears next to the brilliant one The main power output is the robustness of the construction: the twelve-cylinder ran smoothly for 20 hours under full load on the test bench. Nothing ever broke down in the race, and after the event, new bearings, pistons, valves and springs were all that was needed and the engine was ready for use again. How indestructible the twelve-cylinderis real, was finally shown when Porsche entered the CanAm series.
With the exhaust gas turbocharging, the Stuttgart-based company broke new ground, but the engine also showed itself completely from this and the power orgies that followed unimpressed. Mechanically, Mezger only changed the intake cam, increased the displacement to 5.4 liters and reduced the compression from 10.5 to 6.5. For this purpose, the cooling air fan has been adapted to the changed performance and now presses 3,100 liters of air per second through the cooling fins.
The Porsche 917 engine briefly produces 1,500 hp
So equipped, the twelve-cylinder in the 1973 season stable 1,100 hp at 1.3 bar boost pressure and also withstood turns of the driver on the turbo steam wheel with the resultant far higher power - one speaks of 1,500 hp for a short time - completely without complaint. This made the 917/30 so superior that the engine was only given a charge air cooler for a record attempt in 1975. 'Before that it wasn't necessary - we had won all the races', grins Mezger.
With the intercooler, Mark Donohue lapped the Talladega Superspeedway at an average of 355.78 km /h - a world record. So it's no wonder that you can still buy T-shirts at American racetracks with the following imprint: “In 1973 the 917/30 with its 1,100 hp twelve-cylinder was the most powerful racing car in the world. It is still today. ”What other car can you say that about?
The designer of the Porsche 917 engine: Hans Mezger
The passionate 911 driver (he moves next to a current Carrera also a model from 1977) was born in 1929 and is one of the fathers of the success of the Porsche brand. When the Swabian received his diploma after studying engineering at the University of Stuttgart, he had 28 job offers - but none from Porsche. But that's where Hans Mezger wanted to go, so he just applied and started his work in Stuttgart-Zuffenhausen in October 1956.
There he initially dealt with the vertical shaft motor and began developing the 911 drive in 1962 one. The six-cylinder is just as much his work as the 917 engine and the TAG Turbo Formula 1 fromthe eighties - every single one of these masterpieces would be enough to look back on a successful life.
Data and facts about the Porsche 917
Engine: (917- Naturally aspirated engine, values for 917/30 in brackets): twelve-cylinder four-stroke V-engine, cylinder angle 180 degrees, bore x stroke 86.8 x 70.4 mm, displacement 4999 cm3, compression 10.5: 1, output 630 hp at 8300 rpm (original variant 85 x 66 mm, 4494 cm3, 580 PS, 917/30: 90 x 70.4 mm, 5374 cm3, 6.5: 1, 1100 PS at 7800 rpm), maximum torque 60 mkg at 6500 /min (917/30: 112 mkg at 6400 /min), magnesium engine housing, two V-shaped hanging valves per combustion chamber, directly actuated via two overhead, gear-driven camshafts per cylinder row, crankshaft with eight slide bearings, central output, mechanical mixture preparation Bosch petrol injection (917/30: two exhaust gas turbochargers, boost pressure 1.3 bar), double ignition, ignition sequence 1-9-5-12-3-8-6-10-2-7-4-11, shaft-driven air cooling Blower e, dry sump lubrication, a pressure pump, six suction pumps, oil content 24 liters, weight 260 kg (917/30: 285 kg)
Power transmission: Three-disc dry clutch, fully synchronized four or Five-speed gearbox (917/30: four-speed gearbox), multi-disc limited slip differential (917/30: rigid through drive), rear-wheel drive Body /chassis: tubular space frame with glued-on plastic body, all-round independent suspension on double wishbones and longitudinal thrust struts, coil springs and hydraulic telescopic shock absorbers, anti-roll bars, Rack and pinion steering, hydraulic disc brakes, light alloy rims, front 10.5 x 15 or 12 x 15 inches, rear 15 x 15 or 17 x 15 inches (917/30: 12 x 15 and 19 x 15 inches), fuel tank 140 liters
Dimensions /weight: Length /width 4,140 /1,975 mm, height 920 mm, wheelbase 2,300 mm, track width front /rear 1,526 /1,533 or 1,564 /1,584 mm, (917/30: 4,562 /2,085 mm, height 1,155 mm, wheelbase 2,500 mm, track front /rear 1. 670 /1,564 mm), weight 800 kg
Top speed: up to 386 km /h (in Le Mans, 917/30: 382 km /h in Talladega).