whats the best size for the piping diameter on an integra LS with just an intake? would i need to replace the cat with a new one? TIA.

 

2.25 or 2.36 (60mm) is fine for your setup. Most of the companies that sell cat-back exhausts (i.e. Greddy, Apex-i, Comptech, RSR, etc) use 60mm piping. You will not need a new cat unless you get a header with a larger diameter collector (such as a JDM ITR - 2.5 inches, or one of the higher priced race headers).

 

thanks for the help.