Yes but have you seen the pipe directly after the headers, it would have to be nearly three inch in diameter, this acts as an expansion chamber allowing the gases somewhere to go quickly before it has to pass through the system, reducing back pressure, also when the gases get pushed into the smaller pipe it incresses the exhaust gas velocity, they use the same principle on gas turbines, plus the standard 2 1/8 system is mandrel bent and has enough flow to handle 250 hp, as for back pressure even a pipe without bends or mufflers has "restriction" or " back pressure" just not nearly as much. For instance a 3" pipe with a constant radius 90deg (mandrel) bend. the 90 deg bend has approximately the same restriction as 9 feet of straight pipe. Also the catalyst ceramic substrate would just about create enough back pressure on its own, and does the CES exhaust remove all the 2 1/8 pipe in the system or does the flanges join onto a 2 1/8 pipe, just curious... and yes i am an exhaust fitter. The CES system sounds like a great exhaust system though, as it performs and is quiet to a certain extent.