We have tested these Audi RSQ8 Downpipes and found increases of around 40-45bhp without tuning and 140bhp+ on a tuned car. Professional installation is recommended as some exhausts sit slightly different from others and can be tight.
If you have a later model car with OPF/PPF filters, they will need coding out, so you will need to find a tuning company that can do this. These will not fit directly into the car; you will need a stage 2 tune.
These should pass an MOT emissions test when fitted. They are road-legal and Euro 5 rated.