Yes, as a matter of fact the HKS Cat Back is 2.250 Dia,with a mount flange that butts up to the stock Cat. So I guess I'll match up to that. thanks Alex Frank 93SE-R In a message dated 1/2/2004 7:35:04 AM Pacific Standard Time, EEYORE5182 writes: should be the same as the diameter of the stock piping... 1 7/8" i think.