If it’s legal in your state, you might as well get an aftermarket catted x pipe and enjoy a power gain going from 2.25” to 2.5” pipes. I’ve had a magnaflow catted x since 2003 and still pass smog without issue.
'01 Mustang GT 5M
Drivetrain:Steeda,Dragon,Accufab,SLP LMII,Magna X,Triax,3.73,PBR/Stoptech/Porterfield,Alum DS
Suspension:MM C/O F 350#,Griggs SFC,MM LCAs,FRPP UCA,MM PHB,Mach1 STB,Prothane SB Bushing,18X9 03 Cobra