Taming Porsche’s 917
Time, circumstances and money often are the mother of compromise. Such was the case of Porsche’s iconic 917, a 12-cylinder, 230 plus mile-an-hour monster that transformed the German manufacturer from a supporting cast member to the star of the sportscar racing in the first years of the 1970s.
In sum, the 917 was a car that shouldn’t have existed, but it did; that it did so was because the men of Porsche exploited the unintended consequences of a rules loophole made by the Federation International de L’Automobile, the overall governing body of the sport to revamp its prototype arena.
At the heart of the matter was the FIA’s overriding desire to rid itself of the American interlopers from Ford and Chevrolet, which trounced their European opposition at Le Mans and elsewhere during the mid 1960’s. After Ford’s second straight Sarthe triumph in 1967 with its seven-liter V-8 Mark IV GT40, the FIA, with less than six months’ notice, summarily slapped a three-liter displacement cap on the sports racers running in the World Manufacturers Championship.
This may have made the governing body happy, but not its promoters, who feared the wouldn’t be enough of the topflight entries to attract the public. To alleviate those fears, the FIA added a second tier prototype division which permitted engines of up to five liters, the caveat being that at least 50 examples of any particular car had to have been built.
What the FIA had in mind were the older, original Ford GT40s which used Dearborn’s small block V-8, and there Lola T70 coupe counterparts, likewise with small block Detroit power. The plan would have worked if Porsche, which was producing between 40 and 50 racers per year, hadn’t taken a closer look at the regulations and decided it wanted in.
As with anything, though, the devil here was in the details, as Hans Mezger, the head of Race Car Design at Porsche then, explains. “There were two choices for us: to build a three-liter car, or a five-liter car. With the minimum set at 50, we decided it was too costly, and therefore pursued the three-liter option which resulted in the 908 that won our first World Manufacturers’ title in 1969. However, after the FIA cut the requirement to 25 in the late winter of 1968, we changed our minds and went to work on developing what became the 917.”
Like all of its predecessors, the new 917 was evolutionary, not revolutionary, building on what had gone before. Indeed, in terms of its body shape, and tubular frame structure, it was nearly identical to the three liter 908, with the exception of having the driver’s compartment moved slightly more forward in order to accommodate the extra length of the new 180 degree V-12, with its unique central power pick up arrangement.
With nearly 600 horsepower on tap almost from the day it first went on the dyno, Mezger’s engine was a huge success. Indeed, such was its output, that the initial version had a displacement of four and a half, not five liters. Unfortunately, if the 12-cylinder was an award winning piece, the same could not be said for the rest of the pumpkin seed shaped car.
The basic problem was the aerodynamics of its low drag body which produced high speed instability, an issue which had likewise plagued the longtail streamliner versions of the 908, and the earlier 907. Using spoilers and winglets as Band-Aids, Porsche had cured much of the problems, making them competitive at Le Mans, which was the one race Porsche so desperately wanted to win.
However, those two latter prototypes were 190 mile an hour vehicles, while the new 917 could push past 230 mph with ease. At that speed, the Band-Aids didn’t work. In fact, about the only factory driver who liked the 917 was Vic Elford, who, as he put it, “knew from the moment I first saw it that I wanted to run it at Le Mans because, in my mind, it truly had the potential to win.”
Even so, Elford was not unaware of the 917’s aero issues. “Going through the ‘kink’ on the Mulsanne straight at Le Mans where you were doing well over 230, you had to be very careful getting off the throttle and onto the brake, lest the back start steering the front.” And, make no mistake about it: Porsche’s primary intention for the 917, like Elford’s, was to claim the company’s first outright victory in the 24 Hour classic.
”The most important thing for us was to win Le Mans. We believed that the longtail was the correct way to go if we were to accomplish that. And I think the fact that Elford and (Richard) Attwood had a commanding lead when they retired after 22 hours in 1969 proved we were correct in maintaining the same basic shape of the earlier cars.”
That was the good side of the equation. The bad was that unlike the 907s and 908s which came in a distinctly different short tail body for the lower speed circuits found on the World Manufacturer’s schedule, the 917 would enjoy no such luxury, a fact vividly remembered by the Porsche engineer.
“Because we were concerned that if we did what we had done with the 907 and 908 using separate long and short tail bodies the FIA might make us build 25 of each, something that was too costly for us to do, we made the longtail a detachable. Section that bolted onto the 917’s short tail decklid. Because of that the decklid had to slope down towards the rear, which we knew was not the optimum for the speeds it could attain on the slower tracks. But, we had to live with it that way even so.”
Moreover, Mezger’s boss, Ferdinand Piech, who was trained as an aeronautical engineer, wanted to keep the 917’s drag as low as possible, despite the fact that its horsepower, unlike that of the 907 and 908, made this unnecessary in its case. In fact the solution was simple: raise the rear portion of the short tail to form a downforce producing wedge. This curative measure had been demonstrated in July, 1969 when Jo Siffert had tested his new 917 Can-Am Spyder at Weissach.
Featuring a slightly raised, open rear tail, similar to the ones found on the McLarens and Lolas then competing in the North American championship, Siffert’s Spyder proved far easier to drive than the short tail coupes with their sloping rear decks. The problem for Mezger and his engineers was that Piech didn’t want to hear any of this.
What the Porsche men needed was for someone else to “discover” the solution and act on it. That someone turned out to be John Horsman, the chief engineer of John Wyer’s Gulf team that was contracted to race the 917 for the factory in 1970 and ’71.
In October, 1969, Horsman and company were introduced to their new car at a test session at the Austrian Zeltwig circuit where, ironically, a 917 coupe had scored the 12 cylinder’s debut triumph the previous August. Led by Mezger’s deputies, Peter Falk and Helmut Flegl, the Porsche delegation arrived with its Can-Am spyder and a truck filled to the brim with all the materials needed to revise the tails of the two coupes Zuffenhausen had brought for the session.
Horsman, who claims he ignored the Spyder completely, discovered that while the noses of the coupes and their windscreens were covered in bugs, their tails were mint, carwash fresh, with no bugs at all on the surfaces. This led to the obvious conclusion that the tails and their spoilers were not in the air stream, and that the only way to correct the problem was to raise their profile.
When the Englishman approached Mess Falk and Flegl, they were only too happy to “accept” his conclusion, opening the doors of the truck to reveal all the materials he and his mechanics would need to transform the tails. The rest is history, the revised coupes whose lap times had been several seconds down to those of the Spyder, now becoming its equal.
The next day the Porsche camp received the brass from Zuffenhausen, who may not have liked the fact that the 917’s drag had been increased, but who accepted the fact that its road holding qualities had been considerably improved. The beast had been tamed, and in the process was to become the dominant car on the Makes tour for the next two years before the FIA banned it at the end of 1971 much to the detriment of sports car racing itself.
Born amidst politics, the 917 thus became a winner through deviousness and intrigue, not to mention the curiosity that has led mankind to improve its lot in life.
Bill Oursler, October 2011