As I was going through some reciepts I got with the car on past service done on the car I found a reciept stating that the stock turbo was replaced with a S5 turbo, is this turbo more efficient or was it most likely done just for a lower mileage turbo?

 

it is slightly more efficent and has different manifold setup, s4 has a twin scroll flapper thing, and the s5 just has adifferent housing setup to make it sort of twin scroll like. ,but the waste gate design is far superior(wont boost creep very much compaired to s4) , either reason is reasonable though.