Ok, I got you. So why a Y pipe on a Vortec? Why not a X pipe. Vortecs were not desinged to run a single exhaust. I guess you could run the 2 front 02 sensors before the Y pipe, and tune out the rear 02 sensors, but it just seams like a waste to me. As Im sure you all ready know, Vortecs have 4 02 sensors. The 2 front sensors adjust fuel trim levels, and the 2 rear 02 sensors read the what oxygen is in the exhaust after the cats, and the ECM looks for the difference. So to do away with the rear 02 sensors, and, or the cats, you need ether 02 simulators, or to have the rear 02 sensors tuned out of the ECM. Just food for thought. I gutted my cats,and made my own simulators.