From the brochure for the Porsche 917:
Porsche Approaches the Higher Limit of Cylinder Capacity.
Since 1967 the limit of the cylinder capacity for the World Championship Endurance races has been 3000 c.c. for sports prototypes and 5000 c.c. for homologated sports cars with a minimum production of 25 items in twelve consecutive months.
Previously, the cylinder capacity of 5000 c.c. was fully utilized only in sports cars with engines of American origin. At the 1969 Geneva Motor Show, Porsche will be the first European automobile factory to present a large-volume sports car, the type 917, which is to be homologated by the F.I.A. (Fédération Internationale de l’Automobile) at the beginning of the current racing season for the classic endurance races.
The 917 has the largest cylinder capacity and is the fastest Porsche which has ever been built. Particularly remarkable is the fact that it is not an experimental model but a real production car. This, because on March 31st 25 cars will be finished and ready to race.
With a top speed of over 320 KPH, a maximum performance of 520 HP, and a body designed in acoordance with the latest aerodynamic principles, the 917 ranks among the high points of the 1969 automobile year.
See the complete scans of Porsche’s 917 brochure at the Old Car Manual Project