Are there any diffrences in the motors other than being JDM an USDM and being vtec an non-vtec?

Also what are piping sizes as in lengths needed for a del sol? Got a del sol with a JDM D15B but doesnt have an exhaust on it. Just header, cat and pipe. Tired of hearing the baffeling from slowing down and the occasional pop when idiling. So planning on buying a Spoon N1 relica exhaust 2.5" inlet but the stock piping is 1.75"....Have a buddy who owns a muffler shop, but said he needs to know what the piping lengths needed so he can order the piping needed for me