From the Y-pipe we went into a 3-inch pipe and a California-legal catalytic converter. California banned sale of catalytic converters to private parties a few years ago because of the albino grub worm or some such thing. The Walker CalCat line cured that and we got our catalytic converter (PN 81919) and 50-series Flowmaster Stainless Steel muffler (PN 853057) from Summit racing as well. The 50-series is just a bit quieter than the 40-series. We picked up weld-in O2 bungs from our local shop because we simply forgot to order them from Summit.