Some of the cars that took part in the 2013 Kop Hill Climb.
Not the Cowley though...

The Kop Hill Climb in the 1920s was just a dirt track up the open scarp of the Chilterns. Its surface was loose, stony, hard and bumpy. Near the top was a rut, that could tear motorcycle tyres off, and a hump that sent many into the air. It was described as rising 304 feet in 3848 feet, 1 in 5 at its steepest, with a competitive section of 2709 feet.
Today it is a road with a smooth tarmac surface, has gentle bends and its verges are wooded. It starts with a gradual slope and is 1 in 6 at the half way mark. The road then eases off before getting even steeper to 1 in 4 for a short section just before the summit.

See just a few of the cars that took part in 2013.... click on an image to enlarge it. The penultimate image is of the flypast of a Spitfire and a Hurricane - you will certainly need to enlarge that one!