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Old 10-31-2005, 10:41 AM
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Porsche 917K

The Porsche 917K

The long road to LeMans

After Porsche burst onto the racing scene in the early 1950s, the German company had slowly, but gradually progressed through the sportscar racing classes with one goal in mind: an overall victory at LeMans. Porsche's first success at the legendary 24 Hours race came in 1952, when a 356 took the victory in the 751 - 1100 cc class. Patiently Porsche developed new racing cars like the 550, which still used many parts from the road going Porsche 356. By the mid-1960s the gap between road and racing cars grew bigger and bigger, and with it the racing successes increased as well.

Ford and Ferrari were fighting for the LeMans victory with very advanced and powerful cars in the mid-1960s. The cars fielded by Porsche were equipped with engines displacing only a fraction of those found in the leading cars. This however did make them more nimble and competitive on tight and curvy tracks. Unfortunately the LeMans track consisted of long straights, best suited to the most powerful of cars. A rule change at the end of the 1967 season seemed to bring Porsche's new three litre racer, the 908 into contention. The old prototype class was abandoned in favour of a limited production 5-litre Sportscar class (Group 4) and a 3-litre Prototype class (Group 6).

Only two cars were built in sufficient numbers (50) to be homologated for Group 4; the Lola T70 and Ford GT40 Mk I. Both cars were powered by 400+ bhp engines, which was too much for the new 908 to compete with on LeMans. A JWA / Gulf entered GT40 took the LeMans win, but chased by two Porsches, victory was closer than ever! A number of manufacturers appealed the new regulations stating that a 50-car production run in one year was too much for a racing car. For 1969 the number was decreased to 25, which opened the door for a number of manufacturers to at least consider designing and building a car to take on the Lolas and Fords.

Decision making time

Under the leadership of Ferdinand Piech, the Porsche racing department had produced a new car almost every year in the mid-1960s. All of them were prototype racers, yet the production reached the now magic figure of 25 almost always, with many cars sold to privateers. Piech figured that if they would build a Group 4 racer, much of the money invested could be earned back from sales to privateers. One of the biggest problems was the enormous and new engine the car would need, especially considering the fact that Porsche's largest engine at the time displaced just under three litres. With little time for testing available, the fact that 25 cars had to be produced before the car could be raced was also a big concern, so the design had to be right straight away.

With less than ten months to go before the 1969 24 Hours of LeMans race, Porsche set out to design the new car, which represented the single biggest step in their racing history. Porsche's strategy of gradual development had served them very well in the past, but Piech understood more was needed now to finally clinch the overall victory. According to very strong rumours Volkswagen funded approximately 2/3s of the costs of the racing program under the sole condition that Porsche would maintain the use of air-cooled engines for their competition cars. A very interesting way of promoting the air-cooled engine, which Volkswagen used in all of their cars of the day.

The birth of a legend

Weight saving was on the top of the list of the designers and all experience Porsche had gathered on exotic materials was used on the '917' as the new car was to be known. Although the tubular frame was almost identical to that of the 908, it was now constructed of aluminum instead of the steel used on the 8-cylinder racer. The chassis lost some of its rigidity compared to the steel one, but its extremely low weight of just 46 kg more than made up for that. Like all racers of the day, the 917 was suspended all-round by fully independent suspension, made up of wishbones. More exotic materials were found here, with the coil springs used being made up of titanium.

The heart of the 917 was its new engine. The engine used identical cylinders to those found on the 908, just four more, giving a twelve cylinder engine displacing just under 4.5 litres. Two things set the new '912' engine apart from the older engines: the design of the crankshaft and of the camshafts. Whereas the 908 used a boxer type crankshaft, the 912 engine was fitted with a crankshaft similar to those found in 'V'-engines, resulting in a relatively shorter engine. The double overhead camshafts were driven from centrally mounted gears, which effectively cut the engine in two six cylinder sections. A long tradition of shaft driven camshafts was abandoned.

Although the flat-12 was relatively short, it was still a huge engine. In order to stick with the 908's wheelbase, the cockpit was moved forward, giving a somewhat akward driving position. A slightly wider body was fitted compared to the 908, to clear the larger engine and wider track. The rear body featured a detachable tail section, which enabled the customer to choose between a high-downforce or a low-drag tail to suit the needs of the track. The rear wing was fitted with movable flaps, similar to the system used on the longtail 908 coupes. Cold air was blown to the engine by a big fan fitted on top of the flat-12.

Homologation time

Although there were rumours about a large Porsche sportscar being constructed, there was no concrete evidence until the wraps were taken off of the 917 at the 1969 Geneva Motorshow. The stunned press realised a new class of racers was born. There was still a long way to go until the 917 could actually race at LeMans. When Porsche was first visited by the CSI homologation inspectors three cars were assembled, 18 being assembled and sets of parts for seven more were present. Porsche argued that they could easily build the 25 cars needed, but would then have to take them apart again to prepare the cars for racing. The inspectors refused to homologate the 917 and demanded to see 25 completed cars.

Porsche took the CSI's request very literally and set out to construct 25 cars. In a stunning three weeks the cars were completed, quite an accomplishment considering one engine alone took 160 man-hours of work to be completed. Porsche lined up the completed cars behind the factory for inspection by the CSI. As of April 1st 1969, the 917 was homologated. Ironically the 917's only true competitor, the Ferrari 512 S, was homologated a year later even though only 17 examples were completed when the CSI visited the factory.
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Old 10-31-2005, 10:43 AM
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Disastrous debut

What was feared from the outset came through, the Porsche 917 didn't work as well on the racing track as it looked to work on the drawing boards. For some reason the handling was terrible and many thought the 580 bhp engine was too much for the lightweight frame. At its competition debut at the Nurburgring 1000km in April 1969, all works drivers preferred the 908 over the 'unsafe' 917. Longtime Ferrari privateer David Piper was flown in at the last minute to drive the 917, which very carefully driven eventually finished eighth. Porsche searched frantically to figure out what caused the unpredictable and dangerous driving characteristics of the 917.

No solution was found yet, but Porsche persisted reasoning that LeMans with its long straights would better suit the 917. They were proven partly right, but it was not a 24 Hours race Porsche would like to be reminded of. Again none of the works drivers were willing to risk it all in the 917. Three cars were entered, with the Ahrens/Stommelen 917 qualifying on pole. Disaster struck when one of the 917s crashed out and killed its British driver. The two remaining cars continued and lead the race for a while, but both cars retired. The Ford GT40 again beat the Porsche 908, but by just 2 seconds, the closest margin ever. Much work was needed to fix whatever was wrong with the 917.

Outside help

For 1970 Porsche decided to leave the running of the 917s to a number of private teams, who would all be fully supported by the factory: Martini Racing, JWA Gulf Racing and Porsche Salzburg. Still franctically looking for the problem that dogged the 917, Porsche together with the private teams were testing the 917 in the fall of 1969. Some of the JWA engineers present were particularly interested in a Porsche 917 CanAm Spyder also being tested. The short-tailed car seemed to handle a lot better than the regular coupes. The spyder's tail did fit so the engineers picked up a saw and cut off the rear section of the tail. A career changing action!

With the revised tail the JWA 917 changed from a handling nightmare to a pretty well-sorted racing car. Porsche picked up on the British team's golden move and produced a set of new tails for the 917. The rebodied cars are commonly referred to as 917K. At least twenty original 917s were brought up to 917K spec and in 1970 another 12 new 917Ks were constructed. The experiments with the bodies did not stop here and various long-tail variants were tried in 1970 and 1971. The final coupe version was the chunky 917/20 raced at LeMans in 1971.

Now that the handling was sorted Porsche set out to explore the boundaries of the engine regulations. Ferrari's upcoming contender was going to be fitted with a five litre engine so to be ready for the new challenge a 4.9 litre version of the engine was created by stroking the engine. A lot more torque and 20 bhp were the result of the work. For 1971 a slightly larger bore brought the engine up to 4.998 litre and 630 bhp. For CanAm racing Porsche developed the most powerful road-racing engine ever, based on the 12 cylinder unit. With two turbos and a displacement of 5.4 litres this behemoth of an engine produced 1100 bhp in racing trim, with a lot more available for qualifying.

Porsche's well deserved LeMans win

Although Ferrari brought out a Group 4 racer of their own in 1970, there was no stopping the 917K on fast tracks and the 908/03 on slower tracks. Compared to the 917K, the Ferrari 512S was both underpowered and overweight. Even before the race, it was almost certain that Porsche would finally win the much coveted 24 Hours of LeMans race. Two questions remained: which semi-works team was going team and with what tail configuration? The JWA team had refused to run the new longtail or LH cars, deeming them too unstable on corners. Both Porsche Salzburg and Martini entered a LH and Porsche Salzburg also fielded a regular 917K.

Ferrari surprised in practice by qualifying one of the 512S models as high as second. In the race, started by Ferry Porsche, the Ferrari's pace was not as good and the fleet of 917s took off. In the lead were the 4.9 engined longtail of Salzburg together with the two JWA cars also powered by the more powerful engine. Various accidents caused by the dismal weather had taken out most of the eleven Ferraris started. Soon after the fastest Porsches and the sole remaining works Ferrari retired or crashed out as well. Two 917s remained to take the first two places, with the Herrmann/Attwood driven Salzburg entered 917K beating the Martini longtail of Larousse and Kaussen.

Right after LeMans Ferrari returned to the drawing boards and designed the lighter and more powerful 512M. Although it was still heavier and less powerful than the Porsches, its more advanced chassis design made sure it was on pace with 917s. In the season's finale at Kyalami, a privately entered 512M took a victory beating a 917K by two laps. Surprisingly Ferrari abandoned the 512M and focussed on a new car for the 1972 World Championship, leaving the 512M to be raced by private teams. Unlike Porsche's privateers, the Ferrari teams didn't get full factory backing and were not really a match for the likes of the multiple LeMans winning JWA team.

For 1971 Porsche had developed a further modified longtail version, which was more stable than the previous type. JWA was convinced of it now as well and fielded two longtail 917s in their traditional Gulf livery. The most advanced 917 on the grid was the Marko/Van Lennep driven, Martini entered 917K, which was the only 917 to ever race with a magnesium frame. Like in so many races before, the very well prepared JWA cars proved to be the fastest of the 917s, but both cars failed to finish, both with an engine failure. This left the victory for the white magnesium 917K entered by Martini.

End of the line

At the end of season, the Group 4 class was abandoned by the sport's governing body, leaving the Porsche 917 obsolete. Instead of building a new car to comply with the 3-litre prototype regalutions set for the 1972 World Championship, Porsche set out to modify the Porsche 917 for the popular North American CanAm championship. The results were again very good, making the 917 in its different guises one of the most successful racing cars ever. By scoring the first of now many Porsche victories at LeMans, the 917 story will always have a gold lining in the German manufacturer's history books.

Pictured are four 917 Ks competing in various rounds of the Classic Endurance Racing (CER) series in 2004 and 2005. Shown in the first six pictures is s/n 020, which took a win in the 1971 Sebring 12 Hours race. Livered in the legendary Gulf colours is s/n 026, an original 917 K, equipped with stability fins on the engine cover. Painted in the psychodelic 'Hippie' colours s/n 021 is seen in action on the Spa Francorchamps track. Seen only in the detail shots is '036', which was later constructed from factory spares.
-Article by Wouter Melissen

For more info and pictures please visit: http://www.ultimatecarpage.com/frame...php&carnum=418
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Old 10-31-2005, 10:46 AM
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Porsche 917K #2:
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Old 10-31-2005, 10:49 AM
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Porsche 917K #3:
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Old 10-31-2005, 10:51 AM
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Porsche 917K #4:
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Old 10-31-2005, 10:54 AM
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Porsche 917K #5:
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Old 10-31-2005, 10:56 AM
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Porsche 917K #6:
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Old 10-31-2005, 10:57 AM
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Porsche 917K #7:
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Old 10-31-2005, 11:13 AM
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wow , wonderful , thanks
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Old 10-31-2005, 03:04 PM
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Nice post McLareN
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Old 10-31-2005, 06:47 PM
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The 917K is one of the best racing cars ever produced
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Old 10-31-2005, 08:01 PM
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Amazing find MclareN!
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Old 11-01-2005, 12:58 AM
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917Kurzheck is probably the nicest ever racecar imo, Langheck isn't bad eighter... Btw. do you have any pics of the Porsche 961 Race car?
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Old 11-01-2005, 01:20 AM
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http://www.imca-slotracing.com/AS70LM.htm
have a look to this site , lots of old pics
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Old 11-01-2005, 10:48 AM
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Quote:
Originally Posted by carweb
917Kurzheck is probably the nicest ever racecar imo, Langheck isn't bad eighter... Btw. do you have any pics of the Porsche 961 Race car?
Porsche 961 Photos

http://www.flat-6.net/forum/showthread.php?t=8394

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