It's a GTI-R T28 kit, and yes it's 3 inch on the cold side.....I went w/ 3" due to the Q45 throttle body, and was also planning ahead for the GT3071R that's going on in about a month or so. If you are going to run a T25 kit 3" piping would be overkill. Before this manifold and Q45 tb, I was running 2.5" piping w/ blow through, and it worked just fine.