You can eliminate the cat (restriction), but you need something in its place to end the tuned portion of the exhasut, i.e. sonic pulse deadener. A resonator section would be fine. All this assuming you can pass emissions. Luckily i don't have that test where i live =). Right now i just have a second high flow muffler where the cat used to be, it kills the pulse and quiets it down a bit, it sould be ungodly loud without something there. EdZ