Hi RickyST,
That's a very good question. Unfortunately we have not tested the down pipe on a stock vehicle. The original prototype volunteer had to sell his ST as he had an addition to his family and required a larger vehicle. The second prototype volunteer who let us borrow their vehicle already had the GReddy Supreme SP exhaust system installed and the factory Ford exhaust system was not available.
With that being said, our Supreme SP was fabricated on a 100% Stock Ford Focus ST and utilizes the factory hanger locations. Again we have not tested our Down Pipe on an ST with a stock exhaust system; but it should be compatible.