How Porsche restored the original 917
We reported last month that Porsche was painstakingly restoring 917-001, the original prototype for the 917 that conquered Le Mans and Can-Am, to celebrate the 50th anniversary of that exact vehicle’s debut at the 1969 Geneva Motor Show. Now, the automaker revealed details on that meticulous restoration, along with a video commemorating 50 years of the 917.
The restoration was complicated by the way race cars used to be treated. Today, a lot of retired race cars go directly to museums or collectors. Half a century ago, racing prototypes were used for development purposes, and that development was so rapid that cars rarely competed in the same exact form from one race to the next. When chassis # 001 was assembled, nobody knew just how successful and iconic the design would turn out to be. Originally built in “longtail” form, #001 was extensively modified to be used as a show car replica after Porsche won the 24 Hours of Le Mans with a shorttail 917 in 1970.
The roof, windshield, doors, and door frames are still original, but to take the first 917 back to how it was on the Geneva stand, restorers had to make a new rear subframe, fabricate new body sections including a detachable longtail, and recreate the original rear-axle kinematic lever system for the rear air flaps. Magnesium wheels are prone to pitting over time, so new rims were also cast using the original designs.
Restoration of 917-001 began in February of 2018 with the dismantling of the car. The team had just 13 months before the planned introduction of the restored car at the 2019 Retro Classics show in Stuttgart. The body and frame were 3D scanned, and CAD data was derived from those scans. By combining that data with the original drawings of the car (archived at the Porsche Museum), technicians were able to machine precise body molds from Ureol polymer, and then lay up the fiberglass with period-correct polyester resin.
By September, the front body section was completed and mounted on the chassis, while the rear frame was returned to original specs. Attention was then turned to the removable rear body section and the car’s original trick air flaps.
The 917 prototype originally featured movable rear air flaps that were kinematically linked to the rear wheel knuckles to keep the 917 stable under cornering and braking while maximizing straightaway speed. When the suspension is compressed, the flaps move to a flatter position to reduce drag. When the rear suspension is unloaded (such as during braking) the flaps move up to increase downforce.
Most people haven’t seen an original longtail with working flaps. Just two weeks before the 1969 Le Mans race, because poorly engineered imitations of the Chaparral 2E “flipper” car’s high wing started flying off F1 cars, the FIA banned movable aerodynamic devices in all racing series under its control. As the original 917 without the flaps was so unstable as to be almost undrivable at speed, Le Mans organizers let it compete for the one race, though neither of the two 917s entered finished the race. The team had rushed to complete the cars before the race and had not yet done sufficient testing and development.
For the 1970 racing season, the rear end of the 917 was redesigned to keep the car stable without the flaps. The car also received the development it needed to become a race winner. As the original had the air flaps, though, 917 chief engineer Hans Mezger is happy that Porsche restored them. “I’m so impressed,” Porsche’s press release quotes him as saying.
Once the body was finished, filler was applied, and then it was block sanded and painted white with a green nose and rear wing struts, just as it had been for its 1969 debut, and Porsche and 917 logos were applied front and back.
The original fabricators had to race the clock to have the car ready for its debut 50 years ago, and once 917-001 was repainted, technicians had just four weeks to complete the restoration and get it running in time for the 2019 Retro Classics show in Stuttgart, held in March.
Now that the Retro Classics show is over, 917-001 will be on permanent display at the Porsche Museum in Stuttgart.