I have a 88 N/A and im looking into getting some custom exhaust made, and I was just curious on what the tube that runs from the engine to the back of the exhaust was?

 

EGR, Exhaust gas recirculation pipe. If your state has emissions laws, better have that included in your exhaust design. If not remove and block that bitch off.

 

split air pipe?

 

block it off on the engine?

 

i'm not familiar with NA's but this page should have what you are looking for...

http://www.2751engineering.com/cart/....php?groupid=4

 

There's no such thing as a "EGR EXHAUST RECIRCULATION PIPE" on an RX-7.

It sounds like what 88 said above if you mean the pipe that connects to a nipple on the catalytic converter. Split Air pipe. Feeds airpump air at a given time to the converter from the ACV.