The title of "world's fastest street legal car" is claimed by a guy in England who has a 1972 Vauxhaul Victor which he calles "Red Victor 1". It has a 9.3L V8 with two turbos, and claims 2200 BHP. 7.8s quarter mile.
The car is street legal because it is grandfathered--and it is also tax free.
Video from YouTube.