Hi i have recently bought a 1987 rx7 s4 N/A. It has no mods, and is bone stock as far as i know. The preivious owner took out the transmission in a crapy way. I have this one hard line that comes out of the back of the engnine and i have no idea what it is. I can not find it in the service manuals at all, maybe im just blind. Any help would be usefull. The part in question is circled in red. The last picture is of the thing from underneath the car where it got mangled even more.

 

split air pipe.
Runs from the engine to the Catalytic converter.
On an S4 it uses the back pressure to activate your 5/6 ports.

 

Thank you so much. I saw it in the manual but wasn't sure.