the modern honeycomb catylist is just not as restrictive as people think, the old thermal reactors sucked so did the ones with the little coated bb's. my 535 had this abortion on it when i got it, no cat a flowmaster then a glass pack in the back, it sounded like ****, after i installed a full exhaust with cat intact it runs better, a certain amount of backpressure helps lowend torque a little anyway