These are nice and sound fantastic.
But the car in the video does not have anything to do with original S1. ProSpeed is Bulgarian company that builds these replicas using old body, they own steel made to fit body"kit" and highly tuned drivetrain from Audi S2.
With todays technology a 1000hp from Audis 2.2L 5 cyl is no problem.. We have many those motors in old Audi 100 sedan running 300km/h (~190mph) in standing mile.
Former world champion rally driver Juha Kankkunen has one original S1 in his collection and he drive it in some events. That is even more nicer than these replicas.
article of his collection