The direct answer is "you don't need one". However. The 2-4oz of gunk collected between oil changes is real. There is not a single argument that says dumping oil gunk into your intake is a good thing so why not remove it? You should get a dual valve catch can such as UPR so you are collecting while under boost. The single valve cans only work when not under boost. Again...it's not necessary but those who have installed...every single one of them..collect some stuff that would have been injected into the intake. Removing it is only a good thing without any drawbacks. Those afraid of the dealer don't know what they are talking about.