Late 70’s Pontiac 400 engine, unsure what this thing is on the side of the block.
Air injection for the exhaust, provides additional oxygen to burn hydrocarbons in the exhaust stream. Did you disconnect the hose?
Must be a Trans Am, looks like an Oldsmobile 403 CID engine.
My thought pcv valve, takes vapors to a filter in the air filter.
The pcv would go where the blue painters tape is on the valve cover.
That’s not a marvel of modern engineering.
The big round thing is a check valve. One that can take the heat from the exhaust. The GM division I worked for made them and the tubes that connected to the exhaust manifold.
@Nevada_545 is correct, the system injects extra air into the exhaust to burn excess hydrocarbons. The exhaust pulses go negative and suck air in past the check valve. When the pulses go positive the valve closes. Clever system.
And I also agree, that is an Oldsmobile 403 V8 and not a real Pontiac 400.
That’s the secondary air injection check valve.
It prevents exhaust gasses from reaching the air pump.
one by pass side vc too.