A quote from the BARC website:
The course itself is a narrow tarmac road about 12 feet wide, 1057 yards from start to finish, rising a total of 140 feet, although uniquely, cars plunge downhill off the startline at Gurston, some accelerating to speeds of around 130 mph in five or six seconds. A tight section of bends brings the cars down to around 25 mph before the uphill blast to the twisty finish line, where the fastest recorded speed is 150 mph....
It's very fast but you won't be troubling the records in a Z!