So, after reading many different articles and talking with people about the GDI motors I decided to install a catch can on my 2017 ST. I went with the McNally Electronics brand (RX Speedworks). Hopefully doing this will reduce the amount of carbon build up on the valves. My car only has a little over 1900 miles on it and I was shocked at the gunk already forming on the valves. You would think manufactures would install a catch can at the factory, but that's a different soap box. I also learned that the 2017 ST is a little different than the 2016 on back. The oil cap is slightly different and the hose going from the valve cover to the turbo inlet is different. This means the hose adapter from RX will not work on the new Focus ST but the 1/2" hose will slide on the small end of the factory hose so it's not a huge deal for right now. The first cylinder and last had the most build up of gunk as you can see in the pictures.