Help ID this part!

frederick_76 nailed it. A freakin' air pump - part of early attempts at smog control. Not needed. MOPAR ones had hard lines going to the back of the exhaust manifold and added more air to the exhaust in attempts to "water down" the emissions. I heard that those could damage the valves if the air pump was unhooked and the piping was left intact. Not sure this was the truth or not. I always tapped them out and put pipe plugs in them.