hi i have an 09 focus st and can buy a focus rs engine and box but i dont no if they will work ok when it comes to mapping the car? can i just get it mapped like an rs as thats the only reason for swapping it so i can get more bhp and dont want to go through all the time and cost for nothing

 

Have a look on STOC mate, there are a few that have been done so one of that cliquey lot will likely know.