We have such a hard time with the epa and the carb board that if we did it it shuts the a-hole politicians up and you will never feel the difference in hp if chosen and placed properly. i am by no means a greenie i love old stuff but if we force them to take notice that our cars are NOT major polluters and we can make a better world for future hot rodders. the old school cats were a joke. the high flow cats i use are obd2 compliant and flow well . i run turbo cars so no restriction in the exhaust means faster spool and no horsepower loss. i have run the car back to back with and without flogging living heel out the car and never noticed any change in drivability,egt's or butt dyno results.