I remember seeing a thread about the different housings between all of the years but can't seem to find it again.

I have a housing with a secondary port below the primary exhaust port on the rotor housing. This is on a 12A motor but can't figure out which generation.

The dumb question is that presumably I cannot build an engine with one housing with the port and one without and run with race headers. The dynamics would be off and I feel like that secondary port would be flowing to open atmosphere.

Where did it come from? What type of exhaust manifold did it have? Has anyone run with different housings with that blocked off?

 

check out Ray Green's 12A teardown thread.

EGR passages can be blocked off. using your header is no problem.

 

79-80 12a. They are for the thermal reactor if I'm not mistaken. You Just install a header right over them and you should be fine as long as your gasket is new.

 

Yep thermal reactor. The correct gasket works fine with a header but a cheaper 81-85 gasket can also work. Now sure for how long. Anyone wanna try?