there was no cat on the stock piping, my friend told me that some model civics dont use a cat bcuz the motors arent that strong (the car is a cx model chassis) so can i just buy a cat and bolt it on to the piping to fill the gap from the exhaust piping up to the headers? and if i do, do i buy a cat for the chassis (CX) or for the motor (DX) ..or are they both the same cat.