OEM head pipes are fine for stock or Stage I motor configurations. However, once cams, head work, more displacement and/or higher compression are part of the new configuration, a "stepped" head pipe, regardles of the system being 2:2; 2:1 or 2:1:2 velocity and removal of exhaust gases and mitigate reversion pulses. Most stepped head pipes will have two steps,1.75" to 1.875"' and a few have 3 steps, the third being 1.876" to 2". Two steps is the most coommon due to the lenght of the head pipe. If looking for an aftermarket exhaust upgrade, look for a stepped head pipe.